Characteristics
A systematic review aims to provide an exhaustive summary of literature relevant to a research question. The first step of a systematic review is a thorough search of the literature for relevant papers. The Methodology section of the review will list the databases and citation indexes searched, such as Web of Science, Embase, and PubMed, as well as any individual journals. Next, the titles and the abstracts of the identified articles are checked against pre-determined criteria for eligibility and relevance. This list will always depend on the research problem. Each included study may be assigned an objective assessment of methodological quality preferably using a method conforming to PRISMA (the current guideline) or the high quality standards of Cochrane collaboration.
Systematic reviews often, but not always, use statistical techniques (meta-analysis) to combine results of the eligible studies, or at least use scoring of the levels of evidence depending on the methodology used. An additional rater may be consulted to resolve any scoring differences between raters. 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 the use of systematic reviews 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 has been influential in developing methods for combining both qualitative and quantitative research in systematic reviews.
Recent developments in systematic reviews include realist reviews, and the meta-narrative approach. These approaches try to overcome the problems of methodological and epistemological heterogeneity in the diverse literatures existing on some subjects. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement suggests a standardized way to ensure a transparent and complete reporting of systematic reviews, and is now required for this kind of research by more than 170 medical journals worldwide.
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