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 relevant research;
• A critical appraisal of the included studies;
• A clear and objective synthesis and presentation of the characteristics and findings of the included studies.

*Lasserson T, Thomas J, Higgins JPT. Chapter 1: Starting a review. In Higgins JPT, Thomas J, Chandler J, Cumpston M, Li T, Page MJ, Welch VA (editors). Cochrane Handbook for Systematic Reviews of Interventions version 6.4 (updated August 2023). Cochrane, 2023. Available from www.training.cochrane.org/handbook.

What is the difference between an evidence synthesis and a systematic review?
A systematic review is a type of evidence synthesis.  Any literature review is a type of evidence synthesis.  For the various types of evidence syntheses/literature reviews, see the page on this guide Types of Reviews.

• Systematic reviews are usually done as a team project, requiring cooperation and a commitment of (lots of) time and effort over an extended period. You will need at least 3 people and, depending on the scope of the project and the size of the database result sets, you should plan for 6-24 months from start to completion.

• Run exploratory searches on the topic to get a sense of the plausibility of your project.

  • 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.

  • Make sure someone else has not already 1) written a recent systematic review on your topic, or 2) is in the midst of a similar systematic review project. Instructions on how to check.

• 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. Look here for database recommendations.

• It is extremely important to develop a protocol for your project.  Guidance is provided here.

• Tools such as a reference manager and a screening tool will save time.