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- October 10, 2023 Issue
October 10, 2023
Literature selections curated by Lewis Flint, MD, FACS, and reviewed by the ACS Brief editorial board.
Multifactorial Quality Improvement Decreases Retained Foreign Objects in OR
Keane OA, Chambers C, Brady CM, et al. Reducing Retained Foreign Objects in the Operating Room: A Quality Improvement Initiative . J Am Coll Surg . 2023; in press.
Editorial: Raval MV. Making Operating Rooms Safer: Communication and Teamwork but Investment in Technologies Is Needed . J Am Coll Surg . 2023; in press.
Although retained foreign object events are unusual in pediatric surgery, they are the most common “never event”—an event that should never happen during surgery—reported to The Joint Commission. The most common retained objects are “soft,” such as sponges, packing, and towels, and these events are associated with significant morbidity for the involved patients. Despite efforts by leading professional organizations such as the ACS, the rate of retained objects has remained stable.
The authors chose the interval between reported retained object events as the index of frequency; they formed a multidisciplinary team to design a multifactor quality improvement initiative including focused quiet time, minimizing interruptions, and closed loop communication during the final surgical count. The initiative was carried out in a single children’s healthcare system. The baseline interval between events was 29 days. After 2 years of improvement cycles, the interval had increased to 451 days. Adherence to the QI protocol was 96.4%.
They concluded that after obtaining buy-in from all participants, the quality improvement initiative was effective.
In the accompanying editorial, Mehul V. Raval, MD, FACS, noted that availability of technology such as RFID chips implanted in sponges, towels, and instruments would further improve these results. Although use of such technology comes with a financial cost, the return on investment could potentially be significant.
Rates of Morbidity and Mortality Associated with Esophageal Perforation Remain Unchanged since 2005
Wong LY, Leipzig M, Liou DZ, et al . Surgical Management of Esophageal Perforation: Examining Trends in a Multi-Institutional Cohort . J Gastrointest Surg . 2023;27(9): 1757-1765.
The study reported in this article reviewed data from the ACS National Surgical Quality Improvement Program database during three eras—2005 to 2009, 2010 to 2014, and 2015 to 2020—to determine changes in mortality and morbidity associated with esophageal perforation, as well as the effects of newer treatment approaches on outcomes.
The study cohort consisted of 378 patients; the main treatment method used was primary repair of the perforation (51%) followed by drainage (24%), resection (18%), and diversion (7%). Rates of primary repair increased during each of the studied intervals. Overall mortality was 9.5%, and the rate of complications was 71%.
When mortality and morbidity rates were examined for each of the chosen eras, there was no significant difference observed. Although primary repair was used more frequently in the latest era, possibly due to the increased usage of indwelling stents, outcomes remained similar.
The authors concluded that even though primary repair is used more frequently in current practice, mortality and morbidity rates for esophageal perforation are significant and have not changed during the 15-year interval of this study.
In This Issue
New Cohort of ACS Academy of Master Surgeon Educators Is Inducted
Sixty-three surgical educators were inducted into the ACS Academy of Master Surgeon Educators® on October 6.
Surgical Quality Partner Store Opens
New store opens giving ACS Surgical Quality Partners access to marketing and communication materials.
Colleague Connection Program Offers Peer Support for Rural and General Surgeons
The ACS Colleague Connection is a platform for surgeons to seek guidance and support from trained Fellows in various areas related to surgical practice.
Take Advantage of Special Registration Rates for Clinical Congress by Wednesday
Register for Clinical Congress 2023 by tomorrow, October 11, to receive an advanced registration discount.
Surgeons Discuss the Cost Implications of Noninvasive Colorectal Cancer Screening Modalities
In this episode of The Operative Word, Dr. Dante Yeh and Dr. Casey Allen discuss Dr. Allen's recent study on cost implications in colorectal cancer screening.
Learn about Changing Paradigms for Next Generation of Lung Transplant Surgeons
The process of selecting donors and, furthermore, the lack of overall quality of donors has led to high waitlist mortality and an overall shortage of suitable allografts. Lung transplantation medicine and surgical science have advanced tremendously over the past decade, and soon could mitigate many of these limitations
Recognize IPV Signs and Symptoms at the Workplace
In October, IPV Awareness Month, surgeons can learn how to recognize IPV in colleagues and patients with ACS resources.
Women Surgeons Share “What I Wish I Knew” in Updated Video Series
The ACS Women in Surgery Committee recently updated its “What I Wish I Knew” video series with additions from four surgeons reflecting on some useful tips and knowledge they’ve learned.
Describes what is involved with conducting a systematic review of the literature for evidence-based public health and how the librarian is a partner in the process.
Several CDC librarians have special training in conducting literature searches for systematic reviews. Literature searches for systematic reviews can take a few weeks to several months from planning to delivery.
Fill out a search request form here or contact the Stephen B. Thacker CDC Library by email [email protected] or telephone 404-639-1717.
Joanna Briggs Institute
Systematic Reviews – CRD’s Guide
Systematic Reviews of Health Promotion and Public Health Interventions
The Guide to Community Preventive Services
Look for systematic reviews that have already been published.
- To ensure that the work has not already been done.
- To provides examples of search strategies for your topic
Look in PROSPERO for registered systematic reviews.
Search Cochrane and CRD-York for systematic reviews.
Search filter for finding systematic reviews in PubMed
Other search filters to locate systematic reviews
A systematic review attempts to collect and analyze all evidence that answers a specific question. The question must be clearly defined and have inclusion and exclusion criteria. A broad and thorough search of the literature is performed and a critical analysis of the search results is reported and ultimately provides a current evidence-based answer to the specific question.
Time: According to Cochrane , it takes 18 months on average to complete a Systematic Review.
The average systematic review from beginning to end requires 18 months of work. “…to find out about a healthcare intervention it is worth searching research literature thoroughly to see if the answer is already known. This may require considerable work over many months…” ( Cochrane Collaboration )
Review Team: Team Members at minimum…
- Content expert
- 2 reviewers
- 1 tie breaker
- 1 statistician (meta-analysis)
- 1 economist if conducting an economic analysis
- *1 librarian (expert searcher) trained in systematic reviews
“Expert searchers are an important part of the systematic review team, crucial throughout the review process-from the development of the proposal and research question to publication.” ( McGowan & Sampson, 2005 )
*Ask your librarian to write a methods section regarding the search methods and to give them co-authorship. You may also want to consider providing a copy of one or all of the search strategies used in an appendix.
The Question to Be Answered: A clearly defined and specific question or questions with inclusion and exclusion criteria.
Written Protocol: Outline the study method, rationale, key questions, inclusion and exclusion criteria, literature searches, data abstraction and data management, analysis of quality of the individual studies, synthesis of data, and grading of the evidience for each key question.
Literature Searches: Search for any systematic reviews that may already answer the key question(s). Next, choose appropriate databases and conduct very broad, comprehensive searches. Search strategies must be documented so that they can be duplicated. The librarian is integral to this step of the process. Before your librarian creates a search strategy and starts searching in earnest you should write a detailed PICO question , determine the inclusion and exclusion criteria for your study, run a preliminary search, and have 2-4 articles that already fit the criteria for your review.
What is searched depends on the topic of the review but should include…
- At least 3 standard medical databases like PubMed/Medline, CINAHL, Embase, etc..
- At least 2 grey literature resources like Clinicaltrials.gov, COS Conference Papers Index, Grey Literature Report, etc…
Citation Management: EndNote is a bibliographic management tools that assist researchers in managing citations. The Stephen B. Thacker CDC Library oversees the site license for EndNote.
To request installation: The library provides EndNote to CDC staff under a site-wide license. Please use the ITSO Software Request Tool (SRT) and submit a request for the latest version (or upgraded version) of EndNote. Please be sure to include the computer name for the workstation where you would like to have the software installed.
EndNote Training: CDC Library offers training on EndNote on a regular basis – both a basic and advanced course. To view the course descriptions and upcoming training dates, please visit the CDC Library training page .
For assistance with EndNote software, please contact [email protected]
Vendor Support and Services: EndNote – Support and Services (Thomson Reuters) EndNote – Tutorials and Live Online Classes (Thomson Reuters)
Articles can be obtained using DocExpress or by searching the electronic journals at the Stephen B. Thacker CDC Library.
IOM Standards for Systematic Reviews: Standard 3.1: Conduct a comprehensive systematic search for evidence
The goal of a systematic review search is to maximize recall and precision while keeping results manageable. Recall (sensitivity) is defined as the number of relevant reports identified divided by the total number of relevant reports in existence. Precision (specificity) is defined as the number of relevant reports identified divided by the total number of reports identified.
Issues to consider when creating a systematic review search:
- All concepts are included in the strategy
- All appropriate subject headings are used
- Appropriate use of explosion
- Appropriate use of subheadings and floating subheadings
- Use of natural language (text words) in addition to controlled vocabulary terms
- Use of appropriate synonyms, acronyms, etc.
- Truncation and spelling variation as appropriate
- Appropriate use of limits such as language, years, etc.
- Field searching, publication type, author, etc.
- Boolean operators used appropriately
- Line errors: when searches are combined using line numbers, be sure the numbers refer to the searches intended
- Check indexing of relevant articles
- Search strategy adapted as needed for multiple databases
For more information on how librarians can assist you with systematic review searching, please check out the following presentation slides given by CDC librarians in 2015 about librarians as collaborators in systematic reviews: Course_LibrarianasCollaborator_SystematicReviews_2015 [PDF – 2 MB]
- Cochrane Handbook: Searching for Studies See Part 2, Chapter 6
A step-by-step guide to systematically identify all relevant animal studies
Materials listed in these guides are selected to provide awareness of quality public health literature and resources. A material’s inclusion does not necessarily represent the views of the U.S. Department of Health and Human Services (HHS), the Public Health Service (PHS), or the Centers for Disease Control and Prevention (CDC), nor does it imply endorsement of the material’s methods or findings. HHS, PHS, and CDC assume no responsibility for the factual accuracy of the items presented. The selection, omission, or content of items does not imply any endorsement or other position taken by HHS, PHS, and CDC. Opinion, findings, and conclusions expressed by the original authors of items included in these materials, or persons quoted therein, are strictly their own and are in no way meant to represent the opinion or views of HHS, PHS, or CDC. References to publications, news sources, and non-CDC Websites are provided solely for informational purposes and do not imply endorsement by HHS, PHS, or CDC.
Exit Notification / Disclaimer Policy
- The Centers for Disease Control and Prevention (CDC) cannot attest to the accuracy of a non-federal website.
- Linking to a non-federal website does not constitute an endorsement by CDC or any of its employees of the sponsors or the information and products presented on the website.
- CDC is not responsible for Section 508 compliance (accessibility) on other federal or private website.
- MEDLINE Home
- About Overview MEDLINE History MEDLINE Journal Selection Statistics Recently Accepted Journals FAQ
- Journal Selection How to Include a Journal in MEDLINE Journal Selection for MEDLINE Literature Selection Technical Review Committee (LSTRC)
MEDLINE is the National Library of Medicine's (NLM) premier bibliographic database that contains references to journal articles in life sciences, with a concentration on biomedicine.
MEDLINE content is searchable via PubMed and constitutes the primary component of PubMed, a literature database developed and maintained by the NLM National Center for Biotechnology Information (NCBI).
Last Reviewed: February 10, 2021
Ambulatory management of gastrointestinal emergencies: what are the current literature data?
- 1 Service de chirurgie digestive et métabolique, CHU d'Amiens, 80054 Amiens, France; Université de Picardie, 80000 Amiens, France.
- 2 Université de Picardie, 80000 Amiens, France; Departement d'anesthésie-réanimation, CHU d'Amiens, 80054 Amiens, France.
- 3 Service des urgences, CHU d'Amiens, 80054 Amiens, France.
- 4 Service de chirurgie digestive et métabolique, CHU d'Amiens, 80054 Amiens, France; Université de Picardie, 80000 Amiens, France. Electronic address: [email protected].
- PMID: 24360353
- DOI: 10.1016/j.jviscsurg.2013.10.007
Introduction: Ambulatory management is a modality of care defined in France by a hospitalization of less than 12h without an overnight stay. Currently, few data are available on its role in the management of gastrointestinal emergencies, such as appendectomy for acute appendicitis, cholecystectomy for acute cholecystitis or emergency proctologic surgery. The aim of this systematic review was to study the published data regarding the feasibility of ambulatory management of emergency visceral surgery and to enquire about the possibilities of further development of this form of management.
Materials and methods: A literature search was conducted from the PubMed(®) databank taking into account all published data up to July 2013.
Results: For acute appendicitis, the success rate of short-stay hospitalization was 72% with unplanned read-mission rates ranging from 0 to 53%, a rate of unscheduled consultations ranging from 0 to 11%, and unplanned inpatient hospitalization rates ranging from 0% to 5%. For acute cholecystitis and proctology, there are few published data.
Conclusion: Ambulatory management has been sparingly studied in the setting of gastrointestinal surgical emergencies. However, there is probably a place for development of this form of management.
Keywords: Emergency; Gastrointestinal surgery; Outpatient management.
Copyright © 2013 Elsevier Masson SAS. All rights reserved.
- Systematic Review
- Ambulatory Surgical Procedures*
- Appendectomy / methods*
- Appendicitis / surgery*
- Cholecystectomy / methods*
- Cholecystitis, Acute / surgery*
- Treatment Outcome
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Lau F, Kuziemsky C, editors. Handbook of eHealth Evaluation: An Evidence-based Approach [Internet]. Victoria (BC): University of Victoria; 2017 Feb 27.
Handbook of eHealth Evaluation: An Evidence-based Approach [Internet].
Chapter 9 methods for literature reviews.
Guy Paré and Spyros Kitsiou .
Literature reviews play a critical role in scholarship because science remains, first and foremost, a cumulative endeavour ( vom Brocke et al., 2009 ). As in any academic discipline, rigorous knowledge syntheses are becoming indispensable in keeping up with an exponentially growing eHealth literature, assisting practitioners, academics, and graduate students in finding, evaluating, and synthesizing the contents of many empirical and conceptual papers. Among other methods, literature reviews are essential for: (a) identifying what has been written on a subject or topic; (b) determining the extent to which a specific research area reveals any interpretable trends or patterns; (c) aggregating empirical findings related to a narrow research question to support evidence-based practice; (d) generating new frameworks and theories; and (e) identifying topics or questions requiring more investigation ( Paré, Trudel, Jaana, & Kitsiou, 2015 ).
Literature reviews can take two major forms. The most prevalent one is the “literature review” or “background” section within a journal paper or a chapter in a graduate thesis. This section synthesizes the extant literature and usually identifies the gaps in knowledge that the empirical study addresses ( Sylvester, Tate, & Johnstone, 2013 ). It may also provide a theoretical foundation for the proposed study, substantiate the presence of the research problem, justify the research as one that contributes something new to the cumulated knowledge, or validate the methods and approaches for the proposed study ( Hart, 1998 ; Levy & Ellis, 2006 ).
The second form of literature review, which is the focus of this chapter, constitutes an original and valuable work of research in and of itself ( Paré et al., 2015 ). Rather than providing a base for a researcher’s own work, it creates a solid starting point for all members of the community interested in a particular area or topic ( Mulrow, 1987 ). The so-called “review article” is a journal-length paper which has an overarching purpose to synthesize the literature in a field, without collecting or analyzing any primary data ( Green, Johnson, & Adams, 2006 ).
When appropriately conducted, review articles represent powerful information sources for practitioners looking for state-of-the art evidence to guide their decision-making and work practices ( Paré et al., 2015 ). Further, high-quality reviews become frequently cited pieces of work which researchers seek out as a first clear outline of the literature when undertaking empirical studies ( Cooper, 1988 ; Rowe, 2014 ). Scholars who track and gauge the impact of articles have found that review papers are cited and downloaded more often than any other type of published article ( Cronin, Ryan, & Coughlan, 2008 ; Montori, Wilczynski, Morgan, Haynes, & Hedges, 2003 ; Patsopoulos, Analatos, & Ioannidis, 2005 ). The reason for their popularity may be the fact that reading the review enables one to have an overview, if not a detailed knowledge of the area in question, as well as references to the most useful primary sources ( Cronin et al., 2008 ). Although they are not easy to conduct, the commitment to complete a review article provides a tremendous service to one’s academic community ( Paré et al., 2015 ; Petticrew & Roberts, 2006 ). Most, if not all, peer-reviewed journals in the fields of medical informatics publish review articles of some type.
The main objectives of this chapter are fourfold: (a) to provide an overview of the major steps and activities involved in conducting a stand-alone literature review; (b) to describe and contrast the different types of review articles that can contribute to the eHealth knowledge base; (c) to illustrate each review type with one or two examples from the eHealth literature; and (d) to provide a series of recommendations for prospective authors of review articles in this domain.
9.2. Overview of the Literature Review Process and Steps
As explained in Templier and Paré (2015) , there are six generic steps involved in conducting a review article:
- formulating the research question(s) and objective(s),
- searching the extant literature,
- screening for inclusion,
- assessing the quality of primary studies,
- extracting data, and
- analyzing data.
Although these steps are presented here in sequential order, one must keep in mind that the review process can be iterative and that many activities can be initiated during the planning stage and later refined during subsequent phases ( Finfgeld-Connett & Johnson, 2013 ; Kitchenham & Charters, 2007 ).
Formulating the research question(s) and objective(s): As a first step, members of the review team must appropriately justify the need for the review itself ( Petticrew & Roberts, 2006 ), identify the review’s main objective(s) ( Okoli & Schabram, 2010 ), and define the concepts or variables at the heart of their synthesis ( Cooper & Hedges, 2009 ; Webster & Watson, 2002 ). Importantly, they also need to articulate the research question(s) they propose to investigate ( Kitchenham & Charters, 2007 ). In this regard, we concur with Jesson, Matheson, and Lacey (2011) that clearly articulated research questions are key ingredients that guide the entire review methodology; they underscore the type of information that is needed, inform the search for and selection of relevant literature, and guide or orient the subsequent analysis. Searching the extant literature: The next step consists of searching the literature and making decisions about the suitability of material to be considered in the review ( Cooper, 1988 ). There exist three main coverage strategies. First, exhaustive coverage means an effort is made to be as comprehensive as possible in order to ensure that all relevant studies, published and unpublished, are included in the review and, thus, conclusions are based on this all-inclusive knowledge base. The second type of coverage consists of presenting materials that are representative of most other works in a given field or area. Often authors who adopt this strategy will search for relevant articles in a small number of top-tier journals in a field ( Paré et al., 2015 ). In the third strategy, the review team concentrates on prior works that have been central or pivotal to a particular topic. This may include empirical studies or conceptual papers that initiated a line of investigation, changed how problems or questions were framed, introduced new methods or concepts, or engendered important debate ( Cooper, 1988 ). Screening for inclusion: The following step consists of evaluating the applicability of the material identified in the preceding step ( Levy & Ellis, 2006 ; vom Brocke et al., 2009 ). Once a group of potential studies has been identified, members of the review team must screen them to determine their relevance ( Petticrew & Roberts, 2006 ). A set of predetermined rules provides a basis for including or excluding certain studies. This exercise requires a significant investment on the part of researchers, who must ensure enhanced objectivity and avoid biases or mistakes. As discussed later in this chapter, for certain types of reviews there must be at least two independent reviewers involved in the screening process and a procedure to resolve disagreements must also be in place ( Liberati et al., 2009 ; Shea et al., 2009 ). Assessing the quality of primary studies: In addition to screening material for inclusion, members of the review team may need to assess the scientific quality of the selected studies, that is, appraise the rigour of the research design and methods. Such formal assessment, which is usually conducted independently by at least two coders, helps members of the review team refine which studies to include in the final sample, determine whether or not the differences in quality may affect their conclusions, or guide how they analyze the data and interpret the findings ( Petticrew & Roberts, 2006 ). Ascribing quality scores to each primary study or considering through domain-based evaluations which study components have or have not been designed and executed appropriately makes it possible to reflect on the extent to which the selected study addresses possible biases and maximizes validity ( Shea et al., 2009 ). Extracting data: The following step involves gathering or extracting applicable information from each primary study included in the sample and deciding what is relevant to the problem of interest ( Cooper & Hedges, 2009 ). Indeed, the type of data that should be recorded mainly depends on the initial research questions ( Okoli & Schabram, 2010 ). However, important information may also be gathered about how, when, where and by whom the primary study was conducted, the research design and methods, or qualitative/quantitative results ( Cooper & Hedges, 2009 ). Analyzing and synthesizing data : As a final step, members of the review team must collate, summarize, aggregate, organize, and compare the evidence extracted from the included studies. The extracted data must be presented in a meaningful way that suggests a new contribution to the extant literature ( Jesson et al., 2011 ). Webster and Watson (2002) warn researchers that literature reviews should be much more than lists of papers and should provide a coherent lens to make sense of extant knowledge on a given topic. There exist several methods and techniques for synthesizing quantitative (e.g., frequency analysis, meta-analysis) and qualitative (e.g., grounded theory, narrative analysis, meta-ethnography) evidence ( Dixon-Woods, Agarwal, Jones, Young, & Sutton, 2005 ; Thomas & Harden, 2008 ).
9.3. Types of Review Articles and Brief Illustrations
EHealth researchers have at their disposal a number of approaches and methods for making sense out of existing literature, all with the purpose of casting current research findings into historical contexts or explaining contradictions that might exist among a set of primary research studies conducted on a particular topic. Our classification scheme is largely inspired from Paré and colleagues’ (2015) typology. Below we present and illustrate those review types that we feel are central to the growth and development of the eHealth domain.
9.3.1. Narrative Reviews
The narrative review is the “traditional” way of reviewing the extant literature and is skewed towards a qualitative interpretation of prior knowledge ( Sylvester et al., 2013 ). Put simply, a narrative review attempts to summarize or synthesize what has been written on a particular topic but does not seek generalization or cumulative knowledge from what is reviewed ( Davies, 2000 ; Green et al., 2006 ). Instead, the review team often undertakes the task of accumulating and synthesizing the literature to demonstrate the value of a particular point of view ( Baumeister & Leary, 1997 ). As such, reviewers may selectively ignore or limit the attention paid to certain studies in order to make a point. In this rather unsystematic approach, the selection of information from primary articles is subjective, lacks explicit criteria for inclusion and can lead to biased interpretations or inferences ( Green et al., 2006 ). There are several narrative reviews in the particular eHealth domain, as in all fields, which follow such an unstructured approach ( Silva et al., 2015 ; Paul et al., 2015 ).
Despite these criticisms, this type of review can be very useful in gathering together a volume of literature in a specific subject area and synthesizing it. As mentioned above, its primary purpose is to provide the reader with a comprehensive background for understanding current knowledge and highlighting the significance of new research ( Cronin et al., 2008 ). Faculty like to use narrative reviews in the classroom because they are often more up to date than textbooks, provide a single source for students to reference, and expose students to peer-reviewed literature ( Green et al., 2006 ). For researchers, narrative reviews can inspire research ideas by identifying gaps or inconsistencies in a body of knowledge, thus helping researchers to determine research questions or formulate hypotheses. Importantly, narrative reviews can also be used as educational articles to bring practitioners up to date with certain topics of issues ( Green et al., 2006 ).
Recently, there have been several efforts to introduce more rigour in narrative reviews that will elucidate common pitfalls and bring changes into their publication standards. Information systems researchers, among others, have contributed to advancing knowledge on how to structure a “traditional” review. For instance, Levy and Ellis (2006) proposed a generic framework for conducting such reviews. Their model follows the systematic data processing approach comprised of three steps, namely: (a) literature search and screening; (b) data extraction and analysis; and (c) writing the literature review. They provide detailed and very helpful instructions on how to conduct each step of the review process. As another methodological contribution, vom Brocke et al. (2009) offered a series of guidelines for conducting literature reviews, with a particular focus on how to search and extract the relevant body of knowledge. Last, Bandara, Miskon, and Fielt (2011) proposed a structured, predefined and tool-supported method to identify primary studies within a feasible scope, extract relevant content from identified articles, synthesize and analyze the findings, and effectively write and present the results of the literature review. We highly recommend that prospective authors of narrative reviews consult these useful sources before embarking on their work.
Darlow and Wen (2015) provide a good example of a highly structured narrative review in the eHealth field. These authors synthesized published articles that describe the development process of mobile health ( m-health ) interventions for patients’ cancer care self-management. As in most narrative reviews, the scope of the research questions being investigated is broad: (a) how development of these systems are carried out; (b) which methods are used to investigate these systems; and (c) what conclusions can be drawn as a result of the development of these systems. To provide clear answers to these questions, a literature search was conducted on six electronic databases and Google Scholar . The search was performed using several terms and free text words, combining them in an appropriate manner. Four inclusion and three exclusion criteria were utilized during the screening process. Both authors independently reviewed each of the identified articles to determine eligibility and extract study information. A flow diagram shows the number of studies identified, screened, and included or excluded at each stage of study selection. In terms of contributions, this review provides a series of practical recommendations for m-health intervention development.
9.3.2. Descriptive or Mapping Reviews
The primary goal of a descriptive review is to determine the extent to which a body of knowledge in a particular research topic reveals any interpretable pattern or trend with respect to pre-existing propositions, theories, methodologies or findings ( King & He, 2005 ; Paré et al., 2015 ). In contrast with narrative reviews, descriptive reviews follow a systematic and transparent procedure, including searching, screening and classifying studies ( Petersen, Vakkalanka, & Kuzniarz, 2015 ). Indeed, structured search methods are used to form a representative sample of a larger group of published works ( Paré et al., 2015 ). Further, authors of descriptive reviews extract from each study certain characteristics of interest, such as publication year, research methods, data collection techniques, and direction or strength of research outcomes (e.g., positive, negative, or non-significant) in the form of frequency analysis to produce quantitative results ( Sylvester et al., 2013 ). In essence, each study included in a descriptive review is treated as the unit of analysis and the published literature as a whole provides a database from which the authors attempt to identify any interpretable trends or draw overall conclusions about the merits of existing conceptualizations, propositions, methods or findings ( Paré et al., 2015 ). In doing so, a descriptive review may claim that its findings represent the state of the art in a particular domain ( King & He, 2005 ).
In the fields of health sciences and medical informatics, reviews that focus on examining the range, nature and evolution of a topic area are described by Anderson, Allen, Peckham, and Goodwin (2008) as mapping reviews . Like descriptive reviews, the research questions are generic and usually relate to publication patterns and trends. There is no preconceived plan to systematically review all of the literature although this can be done. Instead, researchers often present studies that are representative of most works published in a particular area and they consider a specific time frame to be mapped.
An example of this approach in the eHealth domain is offered by DeShazo, Lavallie, and Wolf (2009). The purpose of this descriptive or mapping review was to characterize publication trends in the medical informatics literature over a 20-year period (1987 to 2006). To achieve this ambitious objective, the authors performed a bibliometric analysis of medical informatics citations indexed in medline using publication trends, journal frequencies, impact factors, Medical Subject Headings (MeSH) term frequencies, and characteristics of citations. Findings revealed that there were over 77,000 medical informatics articles published during the covered period in numerous journals and that the average annual growth rate was 12%. The MeSH term analysis also suggested a strong interdisciplinary trend. Finally, average impact scores increased over time with two notable growth periods. Overall, patterns in research outputs that seem to characterize the historic trends and current components of the field of medical informatics suggest it may be a maturing discipline (DeShazo et al., 2009).
9.3.3. Scoping Reviews
Scoping reviews attempt to provide an initial indication of the potential size and nature of the extant literature on an emergent topic (Arksey & O’Malley, 2005; Daudt, van Mossel, & Scott, 2013 ; Levac, Colquhoun, & O’Brien, 2010). A scoping review may be conducted to examine the extent, range and nature of research activities in a particular area, determine the value of undertaking a full systematic review (discussed next), or identify research gaps in the extant literature ( Paré et al., 2015 ). In line with their main objective, scoping reviews usually conclude with the presentation of a detailed research agenda for future works along with potential implications for both practice and research.
Unlike narrative and descriptive reviews, the whole point of scoping the field is to be as comprehensive as possible, including grey literature (Arksey & O’Malley, 2005). Inclusion and exclusion criteria must be established to help researchers eliminate studies that are not aligned with the research questions. It is also recommended that at least two independent coders review abstracts yielded from the search strategy and then the full articles for study selection ( Daudt et al., 2013 ). The synthesized evidence from content or thematic analysis is relatively easy to present in tabular form (Arksey & O’Malley, 2005; Thomas & Harden, 2008 ).
One of the most highly cited scoping reviews in the eHealth domain was published by Archer, Fevrier-Thomas, Lokker, McKibbon, and Straus (2011) . These authors reviewed the existing literature on personal health record ( phr ) systems including design, functionality, implementation, applications, outcomes, and benefits. Seven databases were searched from 1985 to March 2010. Several search terms relating to phr s were used during this process. Two authors independently screened titles and abstracts to determine inclusion status. A second screen of full-text articles, again by two independent members of the research team, ensured that the studies described phr s. All in all, 130 articles met the criteria and their data were extracted manually into a database. The authors concluded that although there is a large amount of survey, observational, cohort/panel, and anecdotal evidence of phr benefits and satisfaction for patients, more research is needed to evaluate the results of phr implementations. Their in-depth analysis of the literature signalled that there is little solid evidence from randomized controlled trials or other studies through the use of phr s. Hence, they suggested that more research is needed that addresses the current lack of understanding of optimal functionality and usability of these systems, and how they can play a beneficial role in supporting patient self-management ( Archer et al., 2011 ).
9.3.4. Forms of Aggregative Reviews
Healthcare providers, practitioners, and policy-makers are nowadays overwhelmed with large volumes of information, including research-based evidence from numerous clinical trials and evaluation studies, assessing the effectiveness of health information technologies and interventions ( Ammenwerth & de Keizer, 2004 ; Deshazo et al., 2009 ). It is unrealistic to expect that all these disparate actors will have the time, skills, and necessary resources to identify the available evidence in the area of their expertise and consider it when making decisions. Systematic reviews that involve the rigorous application of scientific strategies aimed at limiting subjectivity and bias (i.e., systematic and random errors) can respond to this challenge.
Systematic reviews attempt to aggregate, appraise, and synthesize in a single source all empirical evidence that meet a set of previously specified eligibility criteria in order to answer a clearly formulated and often narrow research question on a particular topic of interest to support evidence-based practice ( Liberati et al., 2009 ). They adhere closely to explicit scientific principles ( Liberati et al., 2009 ) and rigorous methodological guidelines (Higgins & Green, 2008) aimed at reducing random and systematic errors that can lead to deviations from the truth in results or inferences. The use of explicit methods allows systematic reviews to aggregate a large body of research evidence, assess whether effects or relationships are in the same direction and of the same general magnitude, explain possible inconsistencies between study results, and determine the strength of the overall evidence for every outcome of interest based on the quality of included studies and the general consistency among them ( Cook, Mulrow, & Haynes, 1997 ). The main procedures of a systematic review involve:
- Formulating a review question and developing a search strategy based on explicit inclusion criteria for the identification of eligible studies (usually described in the context of a detailed review protocol).
- Searching for eligible studies using multiple databases and information sources, including grey literature sources, without any language restrictions.
- Selecting studies, extracting data, and assessing risk of bias in a duplicate manner using two independent reviewers to avoid random or systematic errors in the process.
- Analyzing data using quantitative or qualitative methods.
- Presenting results in summary of findings tables.
- Interpreting results and drawing conclusions.
Many systematic reviews, but not all, use statistical methods to combine the results of independent studies into a single quantitative estimate or summary effect size. Known as meta-analyses , these reviews use specific data extraction and statistical techniques (e.g., network, frequentist, or Bayesian meta-analyses) to calculate from each study by outcome of interest an effect size along with a confidence interval that reflects the degree of uncertainty behind the point estimate of effect ( Borenstein, Hedges, Higgins, & Rothstein, 2009 ; Deeks, Higgins, & Altman, 2008 ). Subsequently, they use fixed or random-effects analysis models to combine the results of the included studies, assess statistical heterogeneity, and calculate a weighted average of the effect estimates from the different studies, taking into account their sample sizes. The summary effect size is a value that reflects the average magnitude of the intervention effect for a particular outcome of interest or, more generally, the strength of a relationship between two variables across all studies included in the systematic review. By statistically combining data from multiple studies, meta-analyses can create more precise and reliable estimates of intervention effects than those derived from individual studies alone, when these are examined independently as discrete sources of information.
The review by Gurol-Urganci, de Jongh, Vodopivec-Jamsek, Atun, and Car (2013) on the effects of mobile phone messaging reminders for attendance at healthcare appointments is an illustrative example of a high-quality systematic review with meta-analysis. Missed appointments are a major cause of inefficiency in healthcare delivery with substantial monetary costs to health systems. These authors sought to assess whether mobile phone-based appointment reminders delivered through Short Message Service ( sms ) or Multimedia Messaging Service ( mms ) are effective in improving rates of patient attendance and reducing overall costs. To this end, they conducted a comprehensive search on multiple databases using highly sensitive search strategies without language or publication-type restrictions to identify all rct s that are eligible for inclusion. In order to minimize the risk of omitting eligible studies not captured by the original search, they supplemented all electronic searches with manual screening of trial registers and references contained in the included studies. Study selection, data extraction, and risk of bias assessments were performed independently by two coders using standardized methods to ensure consistency and to eliminate potential errors. Findings from eight rct s involving 6,615 participants were pooled into meta-analyses to calculate the magnitude of effects that mobile text message reminders have on the rate of attendance at healthcare appointments compared to no reminders and phone call reminders.
Meta-analyses are regarded as powerful tools for deriving meaningful conclusions. However, there are situations in which it is neither reasonable nor appropriate to pool studies together using meta-analytic methods simply because there is extensive clinical heterogeneity between the included studies or variation in measurement tools, comparisons, or outcomes of interest. In these cases, systematic reviews can use qualitative synthesis methods such as vote counting, content analysis, classification schemes and tabulations, as an alternative approach to narratively synthesize the results of the independent studies included in the review. This form of review is known as qualitative systematic review.
A rigorous example of one such review in the eHealth domain is presented by Mickan, Atherton, Roberts, Heneghan, and Tilson (2014) on the use of handheld computers by healthcare professionals and their impact on access to information and clinical decision-making. In line with the methodological guidelines for systematic reviews, these authors: (a) developed and registered with prospero ( www.crd.york.ac.uk/ prospero / ) an a priori review protocol; (b) conducted comprehensive searches for eligible studies using multiple databases and other supplementary strategies (e.g., forward searches); and (c) subsequently carried out study selection, data extraction, and risk of bias assessments in a duplicate manner to eliminate potential errors in the review process. Heterogeneity between the included studies in terms of reported outcomes and measures precluded the use of meta-analytic methods. To this end, the authors resorted to using narrative analysis and synthesis to describe the effectiveness of handheld computers on accessing information for clinical knowledge, adherence to safety and clinical quality guidelines, and diagnostic decision-making.
In recent years, the number of systematic reviews in the field of health informatics has increased considerably. Systematic reviews with discordant findings can cause great confusion and make it difficult for decision-makers to interpret the review-level evidence ( Moher, 2013 ). Therefore, there is a growing need for appraisal and synthesis of prior systematic reviews to ensure that decision-making is constantly informed by the best available accumulated evidence. Umbrella reviews , also known as overviews of systematic reviews, are tertiary types of evidence synthesis that aim to accomplish this; that is, they aim to compare and contrast findings from multiple systematic reviews and meta-analyses ( Becker & Oxman, 2008 ). Umbrella reviews generally adhere to the same principles and rigorous methodological guidelines used in systematic reviews. However, the unit of analysis in umbrella reviews is the systematic review rather than the primary study ( Becker & Oxman, 2008 ). Unlike systematic reviews that have a narrow focus of inquiry, umbrella reviews focus on broader research topics for which there are several potential interventions ( Smith, Devane, Begley, & Clarke, 2011 ). A recent umbrella review on the effects of home telemonitoring interventions for patients with heart failure critically appraised, compared, and synthesized evidence from 15 systematic reviews to investigate which types of home telemonitoring technologies and forms of interventions are more effective in reducing mortality and hospital admissions ( Kitsiou, Paré, & Jaana, 2015 ).
9.3.5. Realist Reviews
Realist reviews are theory-driven interpretative reviews developed to inform, enhance, or supplement conventional systematic reviews by making sense of heterogeneous evidence about complex interventions applied in diverse contexts in a way that informs policy decision-making ( Greenhalgh, Wong, Westhorp, & Pawson, 2011 ). They originated from criticisms of positivist systematic reviews which centre on their “simplistic” underlying assumptions ( Oates, 2011 ). As explained above, systematic reviews seek to identify causation. Such logic is appropriate for fields like medicine and education where findings of randomized controlled trials can be aggregated to see whether a new treatment or intervention does improve outcomes. However, many argue that it is not possible to establish such direct causal links between interventions and outcomes in fields such as social policy, management, and information systems where for any intervention there is unlikely to be a regular or consistent outcome ( Oates, 2011 ; Pawson, 2006 ; Rousseau, Manning, & Denyer, 2008 ).
To circumvent these limitations, Pawson, Greenhalgh, Harvey, and Walshe (2005) have proposed a new approach for synthesizing knowledge that seeks to unpack the mechanism of how “complex interventions” work in particular contexts. The basic research question — what works? — which is usually associated with systematic reviews changes to: what is it about this intervention that works, for whom, in what circumstances, in what respects and why? Realist reviews have no particular preference for either quantitative or qualitative evidence. As a theory-building approach, a realist review usually starts by articulating likely underlying mechanisms and then scrutinizes available evidence to find out whether and where these mechanisms are applicable ( Shepperd et al., 2009 ). Primary studies found in the extant literature are viewed as case studies which can test and modify the initial theories ( Rousseau et al., 2008 ).
The main objective pursued in the realist review conducted by Otte-Trojel, de Bont, Rundall, and van de Klundert (2014) was to examine how patient portals contribute to health service delivery and patient outcomes. The specific goals were to investigate how outcomes are produced and, most importantly, how variations in outcomes can be explained. The research team started with an exploratory review of background documents and research studies to identify ways in which patient portals may contribute to health service delivery and patient outcomes. The authors identified six main ways which represent “educated guesses” to be tested against the data in the evaluation studies. These studies were identified through a formal and systematic search in four databases between 2003 and 2013. Two members of the research team selected the articles using a pre-established list of inclusion and exclusion criteria and following a two-step procedure. The authors then extracted data from the selected articles and created several tables, one for each outcome category. They organized information to bring forward those mechanisms where patient portals contribute to outcomes and the variation in outcomes across different contexts.
9.3.6. Critical Reviews
Lastly, critical reviews aim to provide a critical evaluation and interpretive analysis of existing literature on a particular topic of interest to reveal strengths, weaknesses, contradictions, controversies, inconsistencies, and/or other important issues with respect to theories, hypotheses, research methods or results ( Baumeister & Leary, 1997 ; Kirkevold, 1997 ). Unlike other review types, critical reviews attempt to take a reflective account of the research that has been done in a particular area of interest, and assess its credibility by using appraisal instruments or critical interpretive methods. In this way, critical reviews attempt to constructively inform other scholars about the weaknesses of prior research and strengthen knowledge development by giving focus and direction to studies for further improvement ( Kirkevold, 1997 ).
Kitsiou, Paré, and Jaana (2013) provide an example of a critical review that assessed the methodological quality of prior systematic reviews of home telemonitoring studies for chronic patients. The authors conducted a comprehensive search on multiple databases to identify eligible reviews and subsequently used a validated instrument to conduct an in-depth quality appraisal. Results indicate that the majority of systematic reviews in this particular area suffer from important methodological flaws and biases that impair their internal validity and limit their usefulness for clinical and decision-making purposes. To this end, they provide a number of recommendations to strengthen knowledge development towards improving the design and execution of future reviews on home telemonitoring.
Table 9.1 outlines the main types of literature reviews that were described in the previous sub-sections and summarizes the main characteristics that distinguish one review type from another. It also includes key references to methodological guidelines and useful sources that can be used by eHealth scholars and researchers for planning and developing reviews.
Typology of Literature Reviews (adapted from Paré et al., 2015).
As shown in Table 9.1 , each review type addresses different kinds of research questions or objectives, which subsequently define and dictate the methods and approaches that need to be used to achieve the overarching goal(s) of the review. For example, in the case of narrative reviews, there is greater flexibility in searching and synthesizing articles ( Green et al., 2006 ). Researchers are often relatively free to use a diversity of approaches to search, identify, and select relevant scientific articles, describe their operational characteristics, present how the individual studies fit together, and formulate conclusions. On the other hand, systematic reviews are characterized by their high level of systematicity, rigour, and use of explicit methods, based on an “a priori” review plan that aims to minimize bias in the analysis and synthesis process (Higgins & Green, 2008). Some reviews are exploratory in nature (e.g., scoping/mapping reviews), whereas others may be conducted to discover patterns (e.g., descriptive reviews) or involve a synthesis approach that may include the critical analysis of prior research ( Paré et al., 2015 ). Hence, in order to select the most appropriate type of review, it is critical to know before embarking on a review project, why the research synthesis is conducted and what type of methods are best aligned with the pursued goals.
9.5. Concluding Remarks
In light of the increased use of evidence-based practice and research generating stronger evidence ( Grady et al., 2011 ; Lyden et al., 2013 ), review articles have become essential tools for summarizing, synthesizing, integrating or critically appraising prior knowledge in the eHealth field. As mentioned earlier, when rigorously conducted review articles represent powerful information sources for eHealth scholars and practitioners looking for state-of-the-art evidence. The typology of literature reviews we used herein will allow eHealth researchers, graduate students and practitioners to gain a better understanding of the similarities and differences between review types.
We must stress that this classification scheme does not privilege any specific type of review as being of higher quality than another ( Paré et al., 2015 ). As explained above, each type of review has its own strengths and limitations. Having said that, we realize that the methodological rigour of any review — be it qualitative, quantitative or mixed — is a critical aspect that should be considered seriously by prospective authors. In the present context, the notion of rigour refers to the reliability and validity of the review process described in section 9.2. For one thing, reliability is related to the reproducibility of the review process and steps, which is facilitated by a comprehensive documentation of the literature search process, extraction, coding and analysis performed in the review. Whether the search is comprehensive or not, whether it involves a methodical approach for data extraction and synthesis or not, it is important that the review documents in an explicit and transparent manner the steps and approach that were used in the process of its development. Next, validity characterizes the degree to which the review process was conducted appropriately. It goes beyond documentation and reflects decisions related to the selection of the sources, the search terms used, the period of time covered, the articles selected in the search, and the application of backward and forward searches ( vom Brocke et al., 2009 ). In short, the rigour of any review article is reflected by the explicitness of its methods (i.e., transparency) and the soundness of the approach used. We refer those interested in the concepts of rigour and quality to the work of Templier and Paré (2015) which offers a detailed set of methodological guidelines for conducting and evaluating various types of review articles.
To conclude, our main objective in this chapter was to demystify the various types of literature reviews that are central to the continuous development of the eHealth field. It is our hope that our descriptive account will serve as a valuable source for those conducting, evaluating or using reviews in this important and growing domain.
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- Cite this Page Paré G, Kitsiou S. Chapter 9 Methods for Literature Reviews. In: Lau F, Kuziemsky C, editors. Handbook of eHealth Evaluation: An Evidence-based Approach [Internet]. Victoria (BC): University of Victoria; 2017 Feb 27.
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A literature review surveys prior research published in books, scholarly articles, and any other sources relevant to a particular issue, area of research, or theory, and by so doing, provides a description, summary, and critical evaluation of these works in relation to the research problem being investigated. Literature reviews are designed to provide an overview of sources you have used in researching a particular topic and to demonstrate to your readers how your research fits within existing scholarship about the topic.
Fink, Arlene. Conducting Research Literature Reviews: From the Internet to Paper . Fourth edition. Thousand Oaks, CA: SAGE, 2014.
Importance of a Good Literature Review
A literature review may consist of simply a summary of key sources, but in the social sciences, a literature review usually has an organizational pattern and combines both summary and synthesis, often within specific conceptual categories . A summary is a recap of the important information of the source, but a synthesis is a re-organization, or a reshuffling, of that information in a way that informs how you are planning to investigate a research problem. The analytical features of a literature review might:
- Give a new interpretation of old material or combine new with old interpretations,
- Trace the intellectual progression of the field, including major debates,
- Depending on the situation, evaluate the sources and advise the reader on the most pertinent or relevant research, or
- Usually in the conclusion of a literature review, identify where gaps exist in how a problem has been researched to date.
Given this, the purpose of a literature review is to:
- Place each work in the context of its contribution to understanding the research problem being studied.
- Describe the relationship of each work to the others under consideration.
- Identify new ways to interpret prior research.
- Reveal any gaps that exist in the literature.
- Resolve conflicts amongst seemingly contradictory previous studies.
- Identify areas of prior scholarship to prevent duplication of effort.
- Point the way in fulfilling a need for additional research.
- Locate your own research within the context of existing literature [very important].
Fink, Arlene. Conducting Research Literature Reviews: From the Internet to Paper. 2nd ed. Thousand Oaks, CA: Sage, 2005; Hart, Chris. Doing a Literature Review: Releasing the Social Science Research Imagination . Thousand Oaks, CA: Sage Publications, 1998; Jesson, Jill. Doing Your Literature Review: Traditional and Systematic Techniques . Los Angeles, CA: SAGE, 2011; Knopf, Jeffrey W. "Doing a Literature Review." PS: Political Science and Politics 39 (January 2006): 127-132; Ridley, Diana. The Literature Review: A Step-by-Step Guide for Students . 2nd ed. Los Angeles, CA: SAGE, 2012.
Types of Literature Reviews
It is important to think of knowledge in a given field as consisting of three layers. First, there are the primary studies that researchers conduct and publish. Second are the reviews of those studies that summarize and offer new interpretations built from and often extending beyond the primary studies. Third, there are the perceptions, conclusions, opinion, and interpretations that are shared informally among scholars that become part of the body of epistemological traditions within the field.
In composing a literature review, it is important to note that it is often this third layer of knowledge that is cited as "true" even though it often has only a loose relationship to the primary studies and secondary literature reviews. Given this, while literature reviews are designed to provide an overview and synthesis of pertinent sources you have explored, there are a number of approaches you could adopt depending upon the type of analysis underpinning your study.
Argumentative Review This form examines literature selectively in order to support or refute an argument, deeply embedded assumption, or philosophical problem already established in the literature. The purpose is to develop a body of literature that establishes a contrarian viewpoint. Given the value-laden nature of some social science research [e.g., educational reform; immigration control], argumentative approaches to analyzing the literature can be a legitimate and important form of discourse. However, note that they can also introduce problems of bias when they are used to make summary claims of the sort found in systematic reviews [see below].
Integrative Review Considered a form of research that reviews, critiques, and synthesizes representative literature on a topic in an integrated way such that new frameworks and perspectives on the topic are generated. The body of literature includes all studies that address related or identical hypotheses or research problems. A well-done integrative review meets the same standards as primary research in regard to clarity, rigor, and replication. This is the most common form of review in the social sciences.
Historical Review Few things rest in isolation from historical precedent. Historical literature reviews focus on examining research throughout a period of time, often starting with the first time an issue, concept, theory, phenomena emerged in the literature, then tracing its evolution within the scholarship of a discipline. The purpose is to place research in a historical context to show familiarity with state-of-the-art developments and to identify the likely directions for future research.
Methodological Review A review does not always focus on what someone said [findings], but how they came about saying what they say [method of analysis]. Reviewing methods of analysis provides a framework of understanding at different levels [i.e. those of theory, substantive fields, research approaches, and data collection and analysis techniques], how researchers draw upon a wide variety of knowledge ranging from the conceptual level to practical documents for use in fieldwork in the areas of ontological and epistemological consideration, quantitative and qualitative integration, sampling, interviewing, data collection, and data analysis. This approach helps highlight ethical issues which you should be aware of and consider as you go through your own study.
Systematic Review This form consists of an overview of existing evidence pertinent to a clearly formulated research question, which uses pre-specified and standardized methods to identify and critically appraise relevant research, and to collect, report, and analyze data from the studies that are included in the review. The goal is to deliberately document, critically evaluate, and summarize scientifically all of the research about a clearly defined research problem . Typically it focuses on a very specific empirical question, often posed in a cause-and-effect form, such as "To what extent does A contribute to B?" This type of literature review is primarily applied to examining prior research studies in clinical medicine and allied health fields, but it is increasingly being used in the social sciences.
Theoretical Review The purpose of this form is to examine the corpus of theory that has accumulated in regard to an issue, concept, theory, phenomena. The theoretical literature review helps to establish what theories already exist, the relationships between them, to what degree the existing theories have been investigated, and to develop new hypotheses to be tested. Often this form is used to help establish a lack of appropriate theories or reveal that current theories are inadequate for explaining new or emerging research problems. The unit of analysis can focus on a theoretical concept or a whole theory or framework.
NOTE : Most often the literature review will incorporate some combination of types. For example, a review that examines literature supporting or refuting an argument, assumption, or philosophical problem related to the research problem will also need to include writing supported by sources that establish the history of these arguments in the literature.
Baumeister, Roy F. and Mark R. Leary. "Writing Narrative Literature Reviews." Review of General Psychology 1 (September 1997): 311-320; Mark R. Fink, Arlene. Conducting Research Literature Reviews: From the Internet to Paper . 2nd ed. Thousand Oaks, CA: Sage, 2005; Hart, Chris. Doing a Literature Review: Releasing the Social Science Research Imagination . Thousand Oaks, CA: Sage Publications, 1998; Kennedy, Mary M. "Defining a Literature." Educational Researcher 36 (April 2007): 139-147; Petticrew, Mark and Helen Roberts. Systematic Reviews in the Social Sciences: A Practical Guide . Malden, MA: Blackwell Publishers, 2006; Torracro, Richard. "Writing Integrative Literature Reviews: Guidelines and Examples." Human Resource Development Review 4 (September 2005): 356-367; Rocco, Tonette S. and Maria S. Plakhotnik. "Literature Reviews, Conceptual Frameworks, and Theoretical Frameworks: Terms, Functions, and Distinctions." Human Ressource Development Review 8 (March 2008): 120-130; Sutton, Anthea. Systematic Approaches to a Successful Literature Review . Los Angeles, CA: Sage Publications, 2016.
Structure and Writing Style
I. Thinking About Your Literature Review
The structure of a literature review should include the following in support of understanding the research problem :
- An overview of the subject, issue, or theory under consideration, along with the objectives of the literature review,
- Division of works under review into themes or categories [e.g. works that support a particular position, those against, and those offering alternative approaches entirely],
- An explanation of how each work is similar to and how it varies from the others,
- Conclusions as to which pieces are best considered in their argument, are most convincing of their opinions, and make the greatest contribution to the understanding and development of their area of research.
The critical evaluation of each work should consider :
- Provenance -- what are the author's credentials? Are the author's arguments supported by evidence [e.g. primary historical material, case studies, narratives, statistics, recent scientific findings]?
- Methodology -- were the techniques used to identify, gather, and analyze the data appropriate to addressing the research problem? Was the sample size appropriate? Were the results effectively interpreted and reported?
- Objectivity -- is the author's perspective even-handed or prejudicial? Is contrary data considered or is certain pertinent information ignored to prove the author's point?
- Persuasiveness -- which of the author's theses are most convincing or least convincing?
- Validity -- are the author's arguments and conclusions convincing? Does the work ultimately contribute in any significant way to an understanding of the subject?
II. Development of the Literature Review
Four Basic Stages of Writing 1. Problem formulation -- which topic or field is being examined and what are its component issues? 2. Literature search -- finding materials relevant to the subject being explored. 3. Data evaluation -- determining which literature makes a significant contribution to the understanding of the topic. 4. Analysis and interpretation -- discussing the findings and conclusions of pertinent literature.
Consider the following issues before writing the literature review: Clarify If your assignment is not specific about what form your literature review should take, seek clarification from your professor by asking these questions: 1. Roughly how many sources would be appropriate to include? 2. What types of sources should I review (books, journal articles, websites; scholarly versus popular sources)? 3. Should I summarize, synthesize, or critique sources by discussing a common theme or issue? 4. Should I evaluate the sources in any way beyond evaluating how they relate to understanding the research problem? 5. Should I provide subheadings and other background information, such as definitions and/or a history? Find Models Use the exercise of reviewing the literature to examine how authors in your discipline or area of interest have composed their literature review sections. Read them to get a sense of the types of themes you might want to look for in your own research or to identify ways to organize your final review. The bibliography or reference section of sources you've already read, such as required readings in the course syllabus, are also excellent entry points into your own research. Narrow the Topic The narrower your topic, the easier it will be to limit the number of sources you need to read in order to obtain a good survey of relevant resources. Your professor will probably not expect you to read everything that's available about the topic, but you'll make the act of reviewing easier if you first limit scope of the research problem. A good strategy is to begin by searching the USC Libraries Catalog for recent books about the topic and review the table of contents for chapters that focuses on specific issues. You can also review the indexes of books to find references to specific issues that can serve as the focus of your research. For example, a book surveying the history of the Israeli-Palestinian conflict may include a chapter on the role Egypt has played in mediating the conflict, or look in the index for the pages where Egypt is mentioned in the text. Consider Whether Your Sources are Current Some disciplines require that you use information that is as current as possible. This is particularly true in disciplines in medicine and the sciences where research conducted becomes obsolete very quickly as new discoveries are made. However, when writing a review in the social sciences, a survey of the history of the literature may be required. In other words, a complete understanding the research problem requires you to deliberately examine how knowledge and perspectives have changed over time. Sort through other current bibliographies or literature reviews in the field to get a sense of what your discipline expects. You can also use this method to explore what is considered by scholars to be a "hot topic" and what is not.
III. Ways to Organize Your Literature Review
Chronology of Events If your review follows the chronological method, you could write about the materials according to when they were published. This approach should only be followed if a clear path of research building on previous research can be identified and that these trends follow a clear chronological order of development. For example, a literature review that focuses on continuing research about the emergence of German economic power after the fall of the Soviet Union. By Publication Order your sources by publication chronology, then, only if the order demonstrates a more important trend. For instance, you could order a review of literature on environmental studies of brown fields if the progression revealed, for example, a change in the soil collection practices of the researchers who wrote and/or conducted the studies. Thematic [“conceptual categories”] A thematic literature review is the most common approach to summarizing prior research in the social and behavioral sciences. Thematic reviews are organized around a topic or issue, rather than the progression of time, although the progression of time may still be incorporated into a thematic review. For example, a review of the Internet’s impact on American presidential politics could focus on the development of online political satire. While the study focuses on one topic, the Internet’s impact on American presidential politics, it would still be organized chronologically reflecting technological developments in media. The difference in this example between a "chronological" and a "thematic" approach is what is emphasized the most: themes related to the role of the Internet in presidential politics. Note that more authentic thematic reviews tend to break away from chronological order. A review organized in this manner would shift between time periods within each section according to the point being made. Methodological A methodological approach focuses on the methods utilized by the researcher. For the Internet in American presidential politics project, one methodological approach would be to look at cultural differences between the portrayal of American presidents on American, British, and French websites. Or the review might focus on the fundraising impact of the Internet on a particular political party. A methodological scope will influence either the types of documents in the review or the way in which these documents are discussed.
Other Sections of Your Literature Review Once you've decided on the organizational method for your literature review, the sections you need to include in the paper should be easy to figure out because they arise from your organizational strategy. In other words, a chronological review would have subsections for each vital time period; a thematic review would have subtopics based upon factors that relate to the theme or issue. However, sometimes you may need to add additional sections that are necessary for your study, but do not fit in the organizational strategy of the body. What other sections you include in the body is up to you. However, only include what is necessary for the reader to locate your study within the larger scholarship about the research problem.
Here are examples of other sections, usually in the form of a single paragraph, you may need to include depending on the type of review you write:
- Current Situation : Information necessary to understand the current topic or focus of the literature review.
- Sources Used : Describes the methods and resources [e.g., databases] you used to identify the literature you reviewed.
- History : The chronological progression of the field, the research literature, or an idea that is necessary to understand the literature review, if the body of the literature review is not already a chronology.
- Selection Methods : Criteria you used to select (and perhaps exclude) sources in your literature review. For instance, you might explain that your review includes only peer-reviewed [i.e., scholarly] sources.
- Standards : Description of the way in which you present your information.
- Questions for Further Research : What questions about the field has the review sparked? How will you further your research as a result of the review?
IV. Writing Your Literature Review
Once you've settled on how to organize your literature review, you're ready to write each section. When writing your review, keep in mind these issues.
Use Evidence A literature review section is, in this sense, just like any other academic research paper. Your interpretation of the available sources must be backed up with evidence [citations] that demonstrates that what you are saying is valid. Be Selective Select only the most important points in each source to highlight in the review. The type of information you choose to mention should relate directly to the research problem, whether it is thematic, methodological, or chronological. Related items that provide additional information, but that are not key to understanding the research problem, can be included in a list of further readings . Use Quotes Sparingly Some short quotes are appropriate if you want to emphasize a point, or if what an author stated cannot be easily paraphrased. Sometimes you may need to quote certain terminology that was coined by the author, is not common knowledge, or taken directly from the study. Do not use extensive quotes as a substitute for using your own words in reviewing the literature. Summarize and Synthesize Remember to summarize and synthesize your sources within each thematic paragraph as well as throughout the review. Recapitulate important features of a research study, but then synthesize it by rephrasing the study's significance and relating it to your own work and the work of others. Keep Your Own Voice While the literature review presents others' ideas, your voice [the writer's] should remain front and center. For example, weave references to other sources into what you are writing but maintain your own voice by starting and ending the paragraph with your own ideas and wording. Use Caution When Paraphrasing When paraphrasing a source that is not your own, be sure to represent the author's information or opinions accurately and in your own words. Even when paraphrasing an author’s work, you still must provide a citation to that work.
V. Common Mistakes to Avoid
These are the most common mistakes made in reviewing social science research literature.
- Sources in your literature review do not clearly relate to the research problem;
- You do not take sufficient time to define and identify the most relevant sources to use in the literature review related to the research problem;
- Relies exclusively on secondary analytical sources rather than including relevant primary research studies or data;
- Uncritically accepts another researcher's findings and interpretations as valid, rather than examining critically all aspects of the research design and analysis;
- Does not describe the search procedures that were used in identifying the literature to review;
- Reports isolated statistical results rather than synthesizing them in chi-squared or meta-analytic methods; and,
- Only includes research that validates assumptions and does not consider contrary findings and alternative interpretations found in the literature.
Cook, Kathleen E. and Elise Murowchick. “Do Literature Review Skills Transfer from One Course to Another?” Psychology Learning and Teaching 13 (March 2014): 3-11; Fink, Arlene. Conducting Research Literature Reviews: From the Internet to Paper . 2nd ed. Thousand Oaks, CA: Sage, 2005; Hart, Chris. Doing a Literature Review: Releasing the Social Science Research Imagination . Thousand Oaks, CA: Sage Publications, 1998; Jesson, Jill. Doing Your Literature Review: Traditional and Systematic Techniques . London: SAGE, 2011; Literature Review Handout. Online Writing Center. Liberty University; Literature Reviews. The Writing Center. University of North Carolina; Onwuegbuzie, Anthony J. and Rebecca Frels. Seven Steps to a Comprehensive Literature Review: A Multimodal and Cultural Approach . Los Angeles, CA: SAGE, 2016; Ridley, Diana. The Literature Review: A Step-by-Step Guide for Students . 2nd ed. Los Angeles, CA: SAGE, 2012; Randolph, Justus J. “A Guide to Writing the Dissertation Literature Review." Practical Assessment, Research, and Evaluation. vol. 14, June 2009; Sutton, Anthea. Systematic Approaches to a Successful Literature Review . Los Angeles, CA: Sage Publications, 2016; Taylor, Dena. The Literature Review: A Few Tips On Conducting It. University College Writing Centre. University of Toronto; Writing a Literature Review. Academic Skills Centre. University of Canberra.
Break Out of Your Disciplinary Box!
Thinking interdisciplinarily about a research problem can be a rewarding exercise in applying new ideas, theories, or concepts to an old problem. For example, what might cultural anthropologists say about the continuing conflict in the Middle East? In what ways might geographers view the need for better distribution of social service agencies in large cities than how social workers might study the issue? You don’t want to substitute a thorough review of core research literature in your discipline for studies conducted in other fields of study. However, particularly in the social sciences, thinking about research problems from multiple vectors is a key strategy for finding new solutions to a problem or gaining a new perspective. Consult with a librarian about identifying research databases in other disciplines; almost every field of study has at least one comprehensive database devoted to indexing its research literature.
Frodeman, Robert. The Oxford Handbook of Interdisciplinarity . New York: Oxford University Press, 2010.
Another Writing Tip
Don't Just Review for Content!
While conducting a review of the literature, maximize the time you devote to writing this part of your paper by thinking broadly about what you should be looking for and evaluating. Review not just what scholars are saying, but how are they saying it. Some questions to ask:
- How are they organizing their ideas?
- What methods have they used to study the problem?
- What theories have been used to explain, predict, or understand their research problem?
- What sources have they cited to support their conclusions?
- How have they used non-textual elements [e.g., charts, graphs, figures, etc.] to illustrate key points?
When you begin to write your literature review section, you'll be glad you dug deeper into how the research was designed and constructed because it establishes a means for developing more substantial analysis and interpretation of the research problem.
Hart, Chris. Doing a Literature Review: Releasing the Social Science Research Imagination . Thousand Oaks, CA: Sage Publications, 1 998.
Yet Another Writing Tip
When Do I Know I Can Stop Looking and Move On?
Here are several strategies you can utilize to assess whether you've thoroughly reviewed the literature:
- Look for repeating patterns in the research findings . If the same thing is being said, just by different people, then this likely demonstrates that the research problem has hit a conceptual dead end. At this point consider: Does your study extend current research? Does it forge a new path? Or, does is merely add more of the same thing being said?
- Look at sources the authors cite to in their work . If you begin to see the same researchers cited again and again, then this is often an indication that no new ideas have been generated to address the research problem.
- Search Google Scholar to identify who has subsequently cited leading scholars already identified in your literature review [see next sub-tab]. This is called citation tracking and there are a number of sources that can help you identify who has cited whom, particularly scholars from outside of your discipline. Here again, if the same authors are being cited again and again, this may indicate no new literature has been written on the topic.
Onwuegbuzie, Anthony J. and Rebecca Frels. Seven Steps to a Comprehensive Literature Review: A Multimodal and Cultural Approach . Los Angeles, CA: Sage, 2016; Sutton, Anthea. Systematic Approaches to a Successful Literature Review . Los Angeles, CA: Sage Publications, 2016.
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[Thoughts delivered at the "What Is Data in Literary Studies?" roundtable at the Modern Language Association Convention in Chicago, IL on 10 January 2014. Roundtable organized by James English.]
Addressing the question, "what is data in literary studies," offers the chance to enlarge our interpretational procedures to include new methods and materials. But also to apply existing methods of analysis to new materials and questions. Quantitative approaches to archives and texts developed by digital humanists have offered one such expansion. These approaches often treat literature as a data mine. In response, I propose that literature is a heuristic for managing and conceptualizing data. In one strain of my current research on how environmental media make claims to knowledge through their form, I locate this heuristic function in climate change fiction and visual culture.
Novels such as Barbara Kingsolver's Flight Behavior , Nathaniel Rich's Odds Against Tomorrow , and Kim Stanley Robinson's Science in the Capital trilogy comprise the knowledge infrastructure of climate crisis. Now, to say that literature is knowledge producing does not mean that it is all-knowing. Just as climate modelers shelve the Enlightenment ideal of certain knowledge,  climate novelists incorporate data with a robust helping of uncertainty. But as part of a knowledge infrastructure, narratives of climate change variously organize and manage data as part of their aesthetic. Devices for information management, they inspire the following methodological question:
How and why might we define the epistemic as a kind of aesthetic?
Kingsolver's 2012 book highlights a version of this problem. The protagonist, Dellarobia, is a stay-at-home mom and lifelong resident of an economically-failing town in Appalachia. About to commit adultery, she stumbles on a wondrous, even miraculous, ecological event: a massive population of monarch butterflies draped like a throbbing, flaming curtain across the forest. Common to other regions, the phenomenon is out of place in Feathertown, Tennessee, but is all the more astounding for that. When an ecologist and his team descend to study the errant migration, Dellarobia learns that the butterflies are a dreadful splendor. In a scene narrating procedures of data collection, she considers that, "if these butterflies were refugees of a horrible misfortune, there could be no beauty in them" (143).
Yet Flight Behavior is a testament to the compatibility of dismaying data and aesthetic beauty. It features dramas of ignorance and attention, of observation and heedlessness, that integrate scientific data and aesthetic experience. The visiting lepidopterist attempts to separate these domains and pronounces, "'Our job is only to describe what exists'" (148). But the novel closes the sharp divide between scientific and aesthetic description. It shows that knowledge only arises through strategies of seeing-as, specifically focalization and simile.
This and other climate novels spark relays between the epistemic and the aesthetic that, for me, invite two inquiries:
First, what are the "epistemic virtues" that fiction espouses, adapts, or challenges? I borrow this concept from Lorraine Daston and Peter Galison's study, Objectivity . They define "epistemic virtues" as "norms that are internalized and enforced by appeal to ethical values, as well as to pragmatic efficacy in securing knowledge." 
Broadening the concept of epistemic virtues to the literary field, then, leads to a second inquiry: in what ways do aesthetic features promote knowledge values? These values might be accuracy, humility, subjectivity, or transparency.
These are large questions that these brief notes can't adequately tackle. Instead, I want to highlight a key narrative device for aesthetically disseminating data and establishing epistemic virtues. That device, I argue, is description.
Description is at once a key site for data dissemination in a text and a site where things are made to matter. It calls on readers to attend to the things of the world and, increasingly, to the numerical data that reference those entities. In Cynthia Wall's account, it is a form of verbal visualization that, emerging from a process of selection, "makes something visible, sets it forth, extracts it from its surroundings, and jabs a finger meaningfully at it."  Description makes things matter then both by manifesting materialities and by giving them affective and epistemic significance.
In essence, description is a narrative apparatus of information and attention control. Re-examining this instrument of attention—especially in contemporary works that bridge science and art—we might theorize data management within literary studies using extant tools of narrative and formal analysis.
 Edwards, Paul N. A Vast Machine: Computer Models, Climate Data, and the Politics of Global Warming (Cambridge, MA: MIT Press, 2010), 435.
 Daston, Lorraine, and Peter Galison. Objectivity (New York: Zone Books, 2010) , 40-41.
 Wall, Cynthia. The Prose of Things: Transformations of Description in the Eighteenth Century (Chicago: University of Chicago Press, 2006), 13.
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- How to Write a Literature Review | Guide, Examples, & Templates
How to Write a Literature Review | Guide, Examples, & Templates
Published on January 2, 2023 by Shona McCombes . Revised on September 11, 2023.
What is a literature review? A literature review is a survey of scholarly sources on a specific topic. It provides an overview of current knowledge, allowing you to identify relevant theories, methods, and gaps in the existing research that you can later apply to your paper, thesis, or dissertation topic .
There are five key steps to writing a literature review:
- Search for relevant literature
- Evaluate sources
- Identify themes, debates, and gaps
- Outline the structure
- Write your literature review
A good literature review doesn’t just summarize sources—it analyzes, synthesizes , and critically evaluates to give a clear picture of the state of knowledge on the subject.
Table of contents
What is the purpose of a literature review, examples of literature reviews, step 1 – search for relevant literature, step 2 – evaluate and select sources, step 3 – identify themes, debates, and gaps, step 4 – outline your literature review’s structure, step 5 – write your literature review, free lecture slides, other interesting articles, frequently asked questions, introduction.
- Quick Run-through
- Step 1 & 2
When you write a thesis , dissertation , or research paper , you will likely have to conduct a literature review to situate your research within existing knowledge. The literature review gives you a chance to:
- Demonstrate your familiarity with the topic and its scholarly context
- Develop a theoretical framework and methodology for your research
- Position your work in relation to other researchers and theorists
- Show how your research addresses a gap or contributes to a debate
- Evaluate the current state of research and demonstrate your knowledge of the scholarly debates around your topic.
Writing literature reviews is a particularly important skill if you want to apply for graduate school or pursue a career in research. We’ve written a step-by-step guide that you can follow below.
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Writing literature reviews can be quite challenging! A good starting point could be to look at some examples, depending on what kind of literature review you’d like to write.
- Example literature review #1: “Why Do People Migrate? A Review of the Theoretical Literature” ( Theoretical literature review about the development of economic migration theory from the 1950s to today.)
- Example literature review #2: “Literature review as a research methodology: An overview and guidelines” ( Methodological literature review about interdisciplinary knowledge acquisition and production.)
- Example literature review #3: “The Use of Technology in English Language Learning: A Literature Review” ( Thematic literature review about the effects of technology on language acquisition.)
- Example literature review #4: “Learners’ Listening Comprehension Difficulties in English Language Learning: A Literature Review” ( Chronological literature review about how the concept of listening skills has changed over time.)
You can also check out our templates with literature review examples and sample outlines at the links below.
Download Word doc Download Google doc
Before you begin searching for literature, you need a clearly defined topic .
If you are writing the literature review section of a dissertation or research paper, you will search for literature related to your research problem and questions .
Make a list of keywords
Start by creating a list of keywords related to your research question. Include each of the key concepts or variables you’re interested in, and list any synonyms and related terms. You can add to this list as you discover new keywords in the process of your literature search.
- Social media, Facebook, Instagram, Twitter, Snapchat, TikTok
- Body image, self-perception, self-esteem, mental health
- Generation Z, teenagers, adolescents, youth
Search for relevant sources
Use your keywords to begin searching for sources. Some useful databases to search for journals and articles include:
- Your university’s library catalogue
- Google Scholar
- Project Muse (humanities and social sciences)
- Medline (life sciences and biomedicine)
- EconLit (economics)
- Inspec (physics, engineering and computer science)
You can also use boolean operators to help narrow down your search.
Make sure to read the abstract to find out whether an article is relevant to your question. When you find a useful book or article, you can check the bibliography to find other relevant sources.
You likely won’t be able to read absolutely everything that has been written on your topic, so it will be necessary to evaluate which sources are most relevant to your research question.
For each publication, ask yourself:
- What question or problem is the author addressing?
- What are the key concepts and how are they defined?
- What are the key theories, models, and methods?
- Does the research use established frameworks or take an innovative approach?
- What are the results and conclusions of the study?
- How does the publication relate to other literature in the field? Does it confirm, add to, or challenge established knowledge?
- What are the strengths and weaknesses of the research?
Make sure the sources you use are credible , and make sure you read any landmark studies and major theories in your field of research.
You can use our template to summarize and evaluate sources you’re thinking about using. Click on either button below to download.
Take notes and cite your sources
As you read, you should also begin the writing process. Take notes that you can later incorporate into the text of your literature review.
It is important to keep track of your sources with citations to avoid plagiarism . It can be helpful to make an annotated bibliography , where you compile full citation information and write a paragraph of summary and analysis for each source. This helps you remember what you read and saves time later in the process.
To begin organizing your literature review’s argument and structure, be sure you understand the connections and relationships between the sources you’ve read. Based on your reading and notes, you can look for:
- Trends and patterns (in theory, method or results): do certain approaches become more or less popular over time?
- Themes: what questions or concepts recur across the literature?
- Debates, conflicts and contradictions: where do sources disagree?
- Pivotal publications: are there any influential theories or studies that changed the direction of the field?
- Gaps: what is missing from the literature? Are there weaknesses that need to be addressed?
This step will help you work out the structure of your literature review and (if applicable) show how your own research will contribute to existing knowledge.
- Most research has focused on young women.
- There is an increasing interest in the visual aspects of social media.
- But there is still a lack of robust research on highly visual platforms like Instagram and Snapchat—this is a gap that you could address in your own research.
There are various approaches to organizing the body of a literature review. Depending on the length of your literature review, you can combine several of these strategies (for example, your overall structure might be thematic, but each theme is discussed chronologically).
The simplest approach is to trace the development of the topic over time. However, if you choose this strategy, be careful to avoid simply listing and summarizing sources in order.
Try to analyze patterns, turning points and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred.
If you have found some recurring central themes, you can organize your literature review into subsections that address different aspects of the topic.
For example, if you are reviewing literature about inequalities in migrant health outcomes, key themes might include healthcare policy, language barriers, cultural attitudes, legal status, and economic access.
If you draw your sources from different disciplines or fields that use a variety of research methods , you might want to compare the results and conclusions that emerge from different approaches. For example:
- Look at what results have emerged in qualitative versus quantitative research
- Discuss how the topic has been approached by empirical versus theoretical scholarship
- Divide the literature into sociological, historical, and cultural sources
A literature review is often the foundation for a theoretical framework . You can use it to discuss various theories, models, and definitions of key concepts.
You might argue for the relevance of a specific theoretical approach, or combine various theoretical concepts to create a framework for your research.
Like any other academic text , your literature review should have an introduction , a main body, and a conclusion . What you include in each depends on the objective of your literature review.
The introduction should clearly establish the focus and purpose of the literature review.
Depending on the length of your literature review, you might want to divide the body into subsections. You can use a subheading for each theme, time period, or methodological approach.
As you write, you can follow these tips:
- Summarize and synthesize: give an overview of the main points of each source and combine them into a coherent whole
- Analyze and interpret: don’t just paraphrase other researchers — add your own interpretations where possible, discussing the significance of findings in relation to the literature as a whole
- Critically evaluate: mention the strengths and weaknesses of your sources
- Write in well-structured paragraphs: use transition words and topic sentences to draw connections, comparisons and contrasts
In the conclusion, you should summarize the key findings you have taken from the literature and emphasize their significance.
When you’ve finished writing and revising your literature review, don’t forget to proofread thoroughly before submitting. Not a language expert? Check out Scribbr’s professional proofreading services !
This article has been adapted into lecture slides that you can use to teach your students about writing a literature review.
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If you want to know more about the research process , methodology , research bias , or statistics , make sure to check out some of our other articles with explanations and examples.
- Sampling methods
- Simple random sampling
- Stratified sampling
- Cluster sampling
- Likert scales
- Null hypothesis
- Statistical power
- Probability distribution
- Effect size
- Poisson distribution
- Optimism bias
- Cognitive bias
- Implicit bias
- Hawthorne effect
- Anchoring bias
- Explicit bias
A literature review is a survey of scholarly sources (such as books, journal articles, and theses) related to a specific topic or research question .
It is often written as part of a thesis, dissertation , or research paper , in order to situate your work in relation to existing knowledge.
There are several reasons to conduct a literature review at the beginning of a research project:
- To familiarize yourself with the current state of knowledge on your topic
- To ensure that you’re not just repeating what others have already done
- To identify gaps in knowledge and unresolved problems that your research can address
- To develop your theoretical framework and methodology
- To provide an overview of the key findings and debates on the topic
Writing the literature review shows your reader how your work relates to existing research and what new insights it will contribute.
The literature review usually comes near the beginning of your thesis or dissertation . After the introduction , it grounds your research in a scholarly field and leads directly to your theoretical framework or methodology .
A literature review is a survey of credible sources on a topic, often used in dissertations , theses, and research papers . Literature reviews give an overview of knowledge on a subject, helping you identify relevant theories and methods, as well as gaps in existing research. Literature reviews are set up similarly to other academic texts , with an introduction , a main body, and a conclusion .
An annotated bibliography is a list of source references that has a short description (called an annotation ) for each of the sources. It is often assigned as part of the research process for a paper .
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November 2023 El Niño update: transport options
El Niño is currently chugging along, and forecasters expect it to continue for the next several months, with a 62% chance of lasting through April–June 2024. Since we’re heading into the winter, when El Niño’s effect on Northern Hemisphere temperature and rain/snow is most distinct, today we’ll drive by some of El Niño’s wide-ranging impacts.
First stop—this El Niño has now met the threshold for a “strong” event! The August–October Oceanic Niño Index, which measures the three-month-average sea surface temperature in the east-central tropical Pacific (the so-called Niño-3.4 region ), was 1.5 °C above the long-term average (long-term is currently 1991–2020). The Oceanic Niño Index is our primary metric for ENSO (El Niño/Southern Oscillation, the entire El Niño and La Niña system). The monthly Niño-3.4 Index was 1.7 °C above average.
2-year history of sea surface temperatures in the Niño-3.4 region of the tropical Pacific for all events evolving into El Niño since 1950 (gray lines) and the current event (purple line). NOAA Climate.gov image based on a graph by Emily Becker and monthly Niño-3.4 index data from CPC using ERSSTv5 .
“Strong” here is in quotation marks because we don’t have an official definition of ENSO strength. Our unofficial thresholds for the strength of an El Niño event are an Oceanic Niño Index of 0.5–0.9 °C for weak, 1.0–1.4 °C for moderate, and above 1.5 °C for strong. Over 2.0 °C is considered “very strong,” or “historically strong.” I’m going to drop the quotation marks going forward, because they slow us down, and we’re motoring here!
We started noting the potential for a strong El Niño way back in April 2023, before El Niño had even arrived (that happened in June ). Currently, forecasters estimate a greater than 55% chance that El Niño will remain above that threshold for strong through January–March 2024. There’s about a 1-in-3 chance that the Oceanic Niño Index will reach 2.0 °C, which has happened four times before in our 73-year record: 1972-73, 1982–83, 1997–98, and 2015–16.
Why does the strength of an El Niño matter? I’ll get to that. First, though, let’s cruise through the reasoning behind the forecast.
I’m on a boat
During an El Niño event, both the tropical Pacific Ocean surface and the atmosphere exhibit characteristic changes. The ocean surface is warmer than average, as I discussed above. Without El Niño, the usual atmospheric pattern, the Walker circulation , consists of rising air and storms over the far western Pacific, west-to-east winds high up in the atmosphere, descending air over the cooler eastern Pacific, and the trade winds, east-to-west winds near the surface.
ENSO-Neutral or average conditions across the tropical Pacific Ocean. Climate.gov schematic by Emily Eng and inspired by NOAA PMEL .
El Niño’s warmer-than-average central and eastern Pacific weaken this pattern, leading to less rain over the far western Pacific, more in the central, and sometimes eastern, Pacific, and weaker trade winds.
El Niño feedbacks between the ocean and atmosphere. During El Niño, the eastward expansion of the convection and rainfall will depend on how warm the absolute sea surface temperatures becomes in the eastern Pacific. This means that during weaker El Niño events, we may only see convection and rainfall increase around the Date Line. But during stronger El Niño events, the increase in convection and rainfall can potentially extend from the Date Line all the way to coastal Ecuador/Peru in South America. Climate.gov schematic by Emily Eng and inspired by NOAA PMEL .
We’ve observed all of these characteristics of the weaker Walker circulation lately, indicating that El Niño’s engine is fully engaged.
The weaker trade winds help to continue and potentially strengthen the ocean surface temperature changes. Under average conditions, consistent trade winds drag across the surface and keep warm water piled up in the far western Pacific. When they weaken, warm water can start to slosh eastward under the surface, in a downwelling Kelvin wave . These waves can take a few months to travel across the Pacific, providing a source of warm water to continue powering the surface warming. Recently, we’ve seen evidence of increased warm water under the surface of the central tropical Pacific, and it appears another downwelling Kelvin wave is in progress.
Water temperatures in the top 300 meters (1,000 feet) of the tropical Pacific Ocean compared to the 1991–2020 average in September–October 2023. NOAA Climate.gov animation, based on data from NOAA's Climate Prediction Center.
Similar to last month, the amount of warm water under the surface isn’t quite up to the October levels seen during the strong El Niño events in 1982, 1997, or 2015. For visuals, you can check out the scatter plot of September values from last month’s blog post , or look at the subsurface cross-sections from October 2023 , 1982 , 1997 , and 2015 . However, another downwelling Kelvin wave would increase the subsurface temperature anomalies in the eastern Pacific.
The strength of an El Niño event matters because the stronger the event, the more likely that we’ll see the characteristic changes in temperature, rain and snow, and other impacts. It doesn’t necessarily mean that the impacts themselves will be so much stronger, but it makes the expected El Niño impacts more likely to happen. Of course, where the weather is concerned, there are no guarantees! However, a stronger El Niño makes it a safer bet that we’ll see the expected patterns.
We’ve written a fair bit about El Niño impacts in our 9.5 years here at the ENSO Blog. Let’s buzz through a few:
- Just a couple weeks ago, Michelle covered El Niño + snow patterns .
- If you’re interested in how El Niño affects the jet stream , check out my recent post.
- How about El Niño and coastal flooding ?
- When I was going nuts from writing about La Niña for three years in a row, I looked into how El Niño (and La Niña!) change the range of winter daily temperatures .
- Here’s a great guest post by Dr. Amy Butler about El Niño and the stratospheric polar vortex.
- Thinking about hopping a flight to Hawaii? Find out about ENSO and Hawaii , courtesy of Nat.
- Hawaii’s too warm for you? Here’s a guest post by Brian Brettschneider on ENSO and Alaska !
- This El Niño has a decent chance of hanging around through March–May, when it could play a role in reducing tornadoes and hail in the south and southeast U.S.
- Tom’s post on the complicated relationship between ENSO and the Indian monsoon is evergreen.
- Does El Niño increase atmospheric rivers ? Nat and his colleague Kai-Chih Tseng investigate.
- El Niño impacts global health ? Yep! Nat has the scoop.
- For the Australian perspective on El Niño , here’s a post by Andrew Watkins.
Our Alaskan friend-of-the-blog, Brian Brettschneider, was kind enough to provide us with maps that show how winter in North America turned out during past El Niños (there have been 29 since 1950) turned out (see footnote). For example, El Niño winters in Florida have more often been wetter (green) than average, while the Midwest has seen more drier-than-average (brown) El Niño winters.
This is not your typical "winter impacts of El Niño" map. It shows the frequency of wet (green) or dry (brown) winters (December-February) across North America during the 29 El Niños from 1940-2022. Places where more than half the El Niño winters were wetter than average by any amount are colored green. (Whether a winter was above- or below-average was based on comparison with a 30-year rolling average centered on the winter in question.) Places where more than half the El Niño winters were drier than average by any amount are colored brown. Much of the southern United States is light or medium green, meaning that wetter-than-average winters were slightly more common than drier-than-average winters. Across the northern part of the contiguous United States, drier-than-average winters slightly outnumbered wet ones. NOAA Climate.gov map, based on analysis of ERA5 data by Brian Brettschneider.
This is not your typical "winter impacts of El Niño" map. The colors show the frequency of cold or warm winters during the 29 El Niños that occurred from 1940-2022. Places where more than half (15 or more) the El Niño winters were cooler than average by any amount are colored blue. (Whether a winter was above- or below-average was based on comparison with a 30-year rolling average centered on the winter in question.) Places where more than half the El Niño winters were warmer than average by any amount are colored red. Most of the United States is light or medium blue, meaning that cooler-than-average winters were slightly more common than warmer-than-average winters. NOAA Climate.gov map, based on analysis of ERA5 data by Brian Brettschneider.
Northwestern North America has seen more warmer (red) than average El Niño winters, and the states around the Gulf of Mexico have been cooler (blue) more often. What do you see? Let us know in the comments!
That’s today’s trip through the wonderful world of ENSO. See you next month!
Rebecca wrote a piece about the summer version of these maps . The maps are based on the “ERA5” reanalysis from the European Center on Medium-range Weather Forecasting, which covers the global climate from January 1940 to the present. A reanalysis is when scientists use a climate model to fill in gaps in past observations. Many observational records are incomplete, due to stations moving, being discontinued, or missing data. Using a climate model, we can connect the dots between missing data and create a continuous record of the past climate. Reanalysis is an invaluable, widely used technique.
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