Systematic Reviews in the Health Sciences

A systematic review, as a type of evidence syntheses, follows a rigorous and structured method with a well-defined, transparent, and replicable process to identify, evaluate, and synthesize the findings of all relevant individual studies on a particular topic or research question.

Key Characteristics:

1. Predefined Protocol: A systematic review is guided by a pre-specified protocol, which outlines the research question, inclusion/exclusion criteria, search strategy, data extraction methods, and analysis plan.
2. Comprehensive Search: It involves a comprehensive and exhaustive search of multiple databases and sources to identify all relevant studies, including unpublished literature (grey literature) to minimize publication bias.
3. Critical Appraisal: Each included study is critically appraised for methodological quality using standardized tools and criteria.
4. Reproducibility: The process is transparent and reproducible, allowing other researchers to follow the same steps and verify the findings.
5. Quantitative Synthesis: A systematic review often includes a meta-analysis, a statistical technique that combines the results of individual studies to provide a pooled estimate of the effect size.

Systematic reviews can be helpful for clinicians who want to integrate research findings into their daily practices, for patients to make well-informed choices about their own care, and for professional medical societies and other organizations that develop clinical practice guidelines. They are useful for:

• Recommendations and guidelines
• Benefit design, coverage and policy decisions
• Public Policy
• Performance Measures
• Research Agendas
• Individual Patient are
• Patient Decisions

DEFINITION 1:  Many systematic reviews contain meta-analyses. Meta-analysis is the use of statistical methods to summarize the results of independent studies. By combining information from all relevant studies, meta-analyses can provide more precise estimates of the effects of health care than those derived from the individual studies included within a review (see Chapter 9, Section 9.1.3). They also facilitate investigations of the consistency of evidence across studies, and the exploration of differences across studies. 

Higgins JPT, Green S (editors). Cochrane Handbook for Systematic Reviews of Interventions Version 5.1.0 [updated March 2011]. The Cochrane Collaboration, 2011. Available from www.cochrane-handbook.org.

DEFINITION 2:  A systematic review is an overview of primary studies that used explicit and reproducible methods.  A meta-analysis is a mathematical synthesis of the results of two or more primary studies that addressed the same hypothesis in the same way.  Although meta-analysis can increase the precision of a result, it is important to ensure that the methods used for the review were valid and reliable. 

Greenhalgh T.  How to read a paper: Papers that summarise other papers (systematic reviews and meta-analyses.) BMJ 1997; Sep 13,315: 672-5 PMID 9310574. 

How to critically appraise a systematic review - Part I < https://youtu.be/NSUk5FLbJoY>

How to critically appraise a systematic review - Part II <https://youtu.be/Ly__U-n4fiQ>

Two short videos by Dr. Shaneyfelt who is an Associate Professor in the Department of Medicine at UAB. He is a general internist who developed a passion for EBM after participating in the McMaster EBM course in 1999. His research interests have focused around clinical practice guidelines and the evaluation & teaching of EBM. He teaches EBM principles to students, residents and faculty. He is a past member of the Society of General Internal Medicine EBM Task Force. He is an associate editor of BMJ EBM journal.