Systematic reviews
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Introduction
A systematic review is a scientific investigation in and of itself with pre-planned methods and an assemblage of original studies as its ‘subject’. Results of multiple primary papers are thus synthesized in the SR, and strategies are used to limit bias and random error. These strategies include a comprehensive search of all potentially relevant articles and the use of explicit, reproducible criteria in the selection of studies for review. Primary research designs and study characteristics are appraised, data are synthesized, and results are interpreted. According to the Dictionary of epidemiology (by Last), 4e (2001), a systematic review is "...the application of strategies that limit bias in the assembly, critical appraisal, and synthesis of all relevant studies on a specific topic. Meta-analysis may be, but is not necessarily, used as part of this process..." More specifically, the Health Technology Assessment (HTA) editorial board says that "...a systematic review is a synthesis that collates all empirical evidence fitting pre-specified eligibility criteria in order to answer a specific research question..." What is a systematic review?A systematic review is an investigation of a clearly-formulated question that uses methodical and explicit steps to identify, select, and critically appraise relevant research, and to collect and analyze data from any appropriate studies that may be found. The process includes a series of searches for papers or studies in reputable biomedical databases (such as PubMed or Embase for medical questions); a comparison of important features of each study against a list of inclusion and/or exclusion criteria (features include study design, subject or medical condition attributes at baseline, details of the exposure or intervention, time factors, etc.); and a detailed critical appraisal of each study for risk of bias and potential confounding factors. Statistical methods (meta-analysis) may or may not be applied to analyze and summarize the results of these included studies. In published reports, systematic reviews explicitly describe the database(s) and key words that were used in the search; the last date databases were searched; study inclusion/exclusion criteria; process for determining inclusion/exclusion, risk of bias/confounding, and data extraction; a list of apparently-relevant studies that were excluded, and reasons for each exclusion; key details of each included study; and summary of findings. Systematic reviews have been described as "...papers that summarize other papers" and "overviews of primary studies that have used explicit and reproducible methods". In SRs, the systematic approach to reviewing the literature is more robust and powerful than in traditional literature reviews, which may be may prone to biases of various kinds (e.g., language, publication, geographic). Further, a systematic review strives to exhaustively search all the relevant peer-reviewed literature as well as grey literature and unpublished research findings. The process by which studies are included or excluded is entirely transparent, and is therefore repeatable for future updating. Cook et al describe SRs as "...scientific investigations in themselves, with pre-planned methods and an assembly of original studies as their “subjects.”" SRs synthesize findings from key, high-powered trials and reports of therapies and interventions using explicit inclusion and exclusion criteria, and may or may not include a meta-analysis. As an approach to gathering, analyzing and synthesizing a body of research, SRs are very popular. SRs include clearly-defined protocols and procedures that ensure accountability and transparency and are typically collaborative in nature. Research teams work in conjunction with a group of professionals, experts and practitioners in the field to ensure that all key resources are located and evaluated. SRs are comprehensive in the way they capture relevant literature yet they often very specific. A set of criteria clearly defines which studies are to be included or excluded in the review - called "inclusion - exclusion" criteria. In the final analysis and synthesis, SRs are evaluated based on methodological rigour and a meta-analysis is conducted when possible. What is the intent of your systematic review?There are at least a dozen systematic review types; note that the most common types conducted in medicine address interventions, prognosis or test accuracy. Is a systematic review appropriate for my (your) research question?
Do you have the team in place to conduct the review?
Is there an existing review?
Do you have sufficient time to conduct the review?
Developing a comprehensive search strategy
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