systematic review - Women

A systematic review is a literature review focused on a research question that tries to identify, appraise, select and synthesize all high quality research evidence relevant to that question. Systematic reviews of high-quality randomized controlled trials are crucial to evidence-based medicine. An understanding of systematic reviews and how to implement them in practice is becoming mandatory for all professionals involved in the delivery of health care. Systematic reviews are not limited to medicine and are quite common in other sciences such as psychology, educational research and sociology. For an example, see the systematic review on the quality of factor analysis by de Vet, Ader, Terwee and Pouwer.

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Characteristics

A systematic review aims to provide an exhaustive summary of literature relevant to a research question. The first step of a systematic review consists of a thorough literature search, usually in the electronic archives like Google Scholar, Web of Science, ScienceDirect, PubMed, Public Library of Science. Next, the titles and the abstracts of the identified articles are checked for eligibility. Third, a list of appraisal criteria is generated to be applied on the selected articles. These criteria usually regard the methodological quality of the studies, the relevance and the credibility that can be attached to the results.. Systematic review often, but not always, uses statistical techniques ( meta-analysis) to combine these valid studies, or at least uses scoring of the levels of evidence depending on the methodology used. Systematic review is often applied in the biomedical or healthcare context, but it can be applied in any field of research. Groups like the Campbell Collaboration are promoting their use in policy-making beyond just healthcare.

A systematic review uses an objective and transparent approach for research synthesis, with the aim of minimizing bias.

While many systematic reviews are based on an explicit quantitative meta-analysis of available data, there are also qualitative reviews which adhere to the standards for gathering, analyzing and reporting evidence. The EPPI-Centre have been influential in developing methods for combining both qualitative and quantitative research in systematic reviews.

Recent developments in systematic reviews include realist reviews, developed by Ray Pawson and Trisha Greenhalgh, and the meta-narrative approach by Greenhalgh and colleagues. These approaches try to overcome the problems of methodological and epistemological heterogeneity in the diverse literatures existing on some subjects.

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Cochrane Collaboration

Many healthcare journals now publish systematic reviews, but the best-known source is The Cochrane Collaboration, a group of over 18,000 specialists in health care who systematically review randomised trials of the effects of prevention, treatments and rehabilitation as well as health systems interventions. When appropriate, they also include the results of other types of research. Cochrane reviews are published in The Cochrane Database of Systematic Reviews section of The Cochrane Library, which to date (July 2010) includes 6244 articles: 4130 reviews; and 1911 protocols for additional reviews being conducted. The 2009 impact factor for The Cochrane Library is 5.653 and it is ranked 11th in the ???Medicine, General & Internal??? category .

The Cochrane Group provides a handbook for systematic reviewers of interventions , where they suggest that each systematic review should contain the following main sections:

Background

Objectives

Methods of the review

Results

Conclusion and discussion

There are seven steps for preparing and maintaining a systematic review, as outlined in the Cochrane Handbook :

Formulating a problem
Locating and selecting studies
Critical appraisal of studies
Collecting data
Analyzing and presenting results
Interpreting results
Improving and updating reviews

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Strengths and weaknesses

While systematic reviews are regarded as the strongest form of medical evidence, a review of 300 studies found that not all systematic reviews were equally reliable, and that their reporting could be improved by a universally agreed upon set of standards and guidelines.

A further study by the same group found that of 100 guidelines reviewed, 4% required updating within a year, and 11% after 2 years; this figure was higher in rapidly-changing fields of medicine, especially cardiovascular medicine. 7% of systematic reviews needed updating at the time of publication. A 2003 study suggested that extending searches beyond major databases, perhaps into gray literature, would increase the effectiveness of reviews.

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