Systematic Reviews & Evidence Synthesis Methods

A systematic review gathers, assesses, and synthesizes all available empirical research on a specific question using a comprehensive search method with an aim to minimize bias.

Or, put another way: 

A systematic review begins with a specific research question.  Authors of the review gather and evaluate all experimental studies that address the question.  Bringing together the findings of these separate studies allows the review authors to make new conclusions from what has been learned.

The key characteristics of a systematic review are:

• A clearly stated set of objectives with pre-defined eligibility criteria for studies;
• An explicit, reproducible methodology;
• A systematic search that attempts to identify all studies that would meet the eligibility criteria;
• A critical appraisal of the included studies;
• A systematic presentation and synthesis of the characteristics and findings of the included studies*.

*Cochrane handbook for systematic reviews of interventions; Version 5.1.0 (updated March 2011).  J. P. T. Higgins and S. Green eds.Cochrane Collaboration, 2011. https://handbook-5-1.cochrane.org/front_page.htm 
 

• Systematic reviews are usually done as a team project, requiring cooperation and a commitment of (lots of) time and effort over an extended period.

• A systematic review requires a research question that is already well-covered in the primary literature.  That is, if there has been little previous work on the topic, there will be little to analyze and conclusions hard to find.

• A narrowly-focused research question may add little to the knowledge of the field of study.

• Team members will need to use research databases for searching the literature.  If these databases are not available through library subscriptions or freely available, their use may require payment or travel.

• Team members should expect that methods used in past studies to investigate the research question will vary.  Preparing for a systematic review includes planning for what can be accepted and what should be excluded.