A systematic review is a review of a clearly formulated question that uses systematic and explicit methods to identify, select, and critically appraise relevant research, and to collect and analyze data from the included studies. Statistical methods (meta-analysis) may or may not be used to analyze and summarize the results of the included studies. Meta-analysis refers to the use of statistical techniques in a systematic review to integrate the results of included studies.1
Systematic reviews differ from traditional narrative reviews and the key characteristics of a systematic review are:
Systematic reviews are the "gold standard" for synthesizing evidence in health because of their rigorous methodology. They are an important source of evidence to guide the development of clinical practice guidelines and to inform clinical decision-making. The first three steps in the Evidence-Based Practice (EBP) process are covered by the process of completing a systematic review - Ask, Acquire, Appraise:
Practitioners (decision-makers) can therefore use systematic reviews to cover the first three steps of the EBP process and then focus their efforts on the subsequent steps of Apply and Audit.2 More generally systematic reviews provide healthcare professionals, consumers, researchers, and policy makers with identified, appraised, and synthesized research-based evidence in an accessible format, therefore saving them considerable time.3
Due to their comprehensive methodology, systematic reviews sit at the top of the research evidence hierarchy, however to be of any use they need to be done well!
By their nature, systematic reviews for publication require a group effort. A typical review team includes a number of team members with a range of skills, including expertise in systematic review methods, information retrieval, the relevant clinical/topic area, statistics, health economics and/or qualitative research methods where appropriate.4 The need to eliminate bias at various stages requires that there be two or more reviewers. Bringing together large teams is resource-intensive and systematic reviews are increasingly being criticised as being too resource intensive and too financially costly.
Typically, a systematic review takes between 9-24 months to complete. There is increasing criticism that due to the length of time taken to complete, evidence from systematic reviews may be out of date and hence may not be relied upon to be accurate.5
Systematic reviews and meta-analyses sit at the top of the evidence hierarchy.
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1. Higgins, P.T., & Green, S. (eds.). (2008). Cochrane handbook for systematic reviews of interventions. Chichester, England ; Hoboken, NJ : Wiley- Blackwell. Available: http://handbook.cochrane.org/
2. O'Connor, E., Whitlock, E., & Spring, B. (2007). Introduction to systematic reviews. Available: http://www.ebbp.org/course_outlines/systematic_review/
3. Mulrow, C.D. (1994). Rationale for systematic reviews. BMJ 309: 597-599. Available: http://www.ncbi.nlm.nih.gov/pubmed/8086953
4. University of York, NHS Centre for Reviews and Dissemination. (2009). Systematic reviews: CRD's guidance for undertaking reviews in health care, 3rd ed. York, England : The Centre. Available: https://www.york.ac.uk/crd/guidance/
5. Brassey, J. (2015). Are you a luddite? Liberating the literature: Some interesting, and not so interesting, issues relating to our work at TRIP Database Ltd. Available: http://blog.tripdatabase.com/2015/08/are-you-luddite.html