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Evaluating Scientific Evidence in Medicine IB 119: Literature Reviews

what is

A literature or systematic review is a published review of literature focused on a research question that identifies, appraises, selects and synthesizes research evidence relevant to the question. Systematic reviews of high-quality randomized controlled trials are crucial to evidence-based medicine.

An understanding of literature or systematic reviews and how to implement them in practice is important for all health professionals. Systematic reviews are not limited to medicine and are common in all other sciences where data are collected, published in the literature, and an assessment of methodological quality for a precisely defined subject would be helpful.

Literature & Systematic Review Resources

Annual Reviews
Annual Reviews Each subject based annual review covers the essential primary research literature referenced within each topic.

BIOSIS Previews
Citations for articles, conference papers, and books on biological and biomedical topics
Coverage: 1926 - present

Cochrane Library
Indexes articles, reviews, and bibliographies which provide evidence-based effects of health care, and published economic evaluations of health care interventions and information on healthcare technology assessment from databases such as The Cochrane Database of Systematic Reviews, Controlled Trials Register, and the Database of Abstracts of Reviews of Effectiveness.
Coverage: date varies

Embase
Search biomedical literature citations for conducting systematic reviews and researching evidence-based medicine. Indexes journals, including many not in Medline and indexes conference abstracts. Broad biomedical scope with strong coverage in drug, pharmaceutical, and toxicological research including economic evaluation.
Coverage: dates vary

PubAg
National Agricultural Library's database search for agricultural information. It is free on the Internet at: http://pubag.nal.usda.gov/.. contains full-text articles relevant to the agricultural sciences, along with citations to peer-reviewed journal articles

PubMed
Use Clinical Queries to retrieve systematic reviews, literature reviews, clinical trials, evidence based information. Use UCB access for UC eLinks to full text articles and citations from MEDLINE, PreMEDLINE, others in medicine and life sciences.
Coverage: 1950 - present dates vary.

PubMed Central (PMC)
A free full-text archive of biomedical and life sciences journal literature at the U.S. National Institutes of Health's National Library of Medicine.
Coverage: dates vary | Full text

Scopus
Indexes journals, conference proceedings, trade publications, and book series in the sciences and more.


Web of Science*
Multidisciplinary. Indexes leading journals in the arts, humanities, sciences and social sciences, search footnotes and  citations. Coverage: 1900 - present

Zoological Record
Covers all aspects of zoology including systematics, ecology, behavior, evolution and conservation

Components

1. Introduction

A literature review surveys scholarly articles, books and other sources (e.g. dissertations, conference proceedings) relevant to a particular issue, area of research, or theory, providing a description, summary, and critical evaluation of each work. The purpose is to offer an overview of significant literature published on a topic.

2. Components

Similar to primary research, development of the literature review has four stages:

  • Problem formulation—which topic or field is being examined and what are its component issues?
  • Literature search—finding materials relevant to the subject being explored
  • Data evaluation—determining which literature makes a significant contribution to the understanding of the topic
  • Analysis and interpretation—discussing the findings and conclusions of pertinent literature

Literature reviews should include the following elements:

  • An overview of the subject, issue or theory under consideration, along with the objectives of the literature review
  • Division of works under review into categories (e.g. those in support of a particular position, those against, and those offering alternative theses entirely)
  • Explanation of how each work is similar to and how it varies from the others
  • Conclusions as to which 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

In assessing each piece, consideration should be given to:

  • 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)?
  • 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/least convincing?
  • Value—Are the author's arguments and conclusions convincing? Does the work ultimately contribute in any significant way to an understanding of the subject?

3. Definition and Use/Purpose

A literature review may be a chapter of a thesis or dissertation, or may be a self-contained review of writings on a subject. In either case, its purpose is to:

  • Place each work in the context of its contribution to the understanding of the subject under review
  • Describe the relationship of each work to the others under consideration
  • Identify new ways to interpret, and shed light on any gaps in, previous research
  • Resolve conflicts amongst seemingly contradictory previous studies
  • Identify areas of prior scholarship to prevent duplication of effort
  • Point the way forward for further research
  • Place one's original work (in the case of theses or dissertations) in the context of existing literature

The literature review itself, however, does not present new primary scholarship.

Steps:

Steps in a systematic review

Step 1: Frame questions for a review
The problems to be addressed by the review should be in the form of clear, structured questions before beginning the review work. Once the review questions have been set, modifications to the protocol should be allowed only if alternative ways of defining the populations, interventions, outcomes or study designs become apparent.|

Step 2: Identify relevant work
The search for studies should be extensive. Multiple resources should be searched without language restrictions. The study selection criteria should flow directly from the review questions and be specified a priori. Reasons for inclusion and exclusion should be recorded.

Step 3: Assess the quality of studies
Study quality assessment is relevant to every step of a review.
Question formulation (Step 1) and study selection criteria (Step 2) should describe the minimum acceptable level of design.
Selected studies should be subjected to a general critical appraisal and design-based quality checklists (Step 3). These detailed quality assessments will be used for exploring heterogeneity and informing decisions regarding suitability of meta-analysis (Step 4). In addition they help in assessing the strength of inferences and making recommendations for future research (Step 5).

Step 4: Summarize the evidence
Data synthesis consists of tabulation of study characteristics, quality and effects as well as use of statistical methods for exploring differences between studies and combining their effects (meta-analysis). Exploration of heterogeneity and its sources should be planned in advance (Step 3). If an overall meta-analysis cannot be done, subgroup meta-analysis may be feasible.

Step 5: Interpret the findings
Be careful of bias. Exploration for heterogeneity should help determine whether the overall summary can be trusted, and, if not, the effects observed in high-quality studies should be used for generating inferences. Any recommendations should be graded by reference to the strengths and weaknesses of the evidence.

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