What is a systematic review?

A systematic review summarises the results of available carefully designed healthcare studies (controlled trials) and provides a high level of evidence on the effectiveness of healthcare interventions. Judgments may be made about the evidence and inform recommendations for healthcare.

These reviews are complicated and depend largely on what clinical trials are available, how they were carried out (the quality of the trials) and the health outcomes that were measured. Review authors pool numerical data about effects of the treatment through a process called meta-analyses. Then authors assess the evidence for any benefits or harms from those treatments. In this way, systematic reviews are able to summarise the existing clinical research on a topic.

The review plan

Review authors set about their task very methodically following, step by step, an advance plan called a protocol. The protocol describes the steps that will be followed when preparing a review. Cochrane protocols are published in the Cochrane Library so that people can provide comments to improve them before the actual review has been conducted.  A protocol describes:

  • the way existing studies are found;
  • how the relevant studies are judged in terms of their usefulness in answering the review question;
  • how the results of the separate studies are brought together to give an overall measure of effectiveness (benefits and harms) - statistical techniques used to combine the results are called meta-analysis.

The review question

The purpose of the review is generally stated as: To assess the effects of [intervention or comparison] for [health problem] in [types of people, disease or problem], and healthcare setting if appropriate. The parts of the review question are often referred to as ‘PICO’ (Participants, Interventions, Comparisons and Outcomes). The included studies generally randomly assign participants to the intervention under investigation or the control or comparative intervention. 

The review title

Titles of Cochrane reviews also have a set layout: Intervention for problem in a disease or population, and sometimes an outcome. An example is:  Surgical excision margins for primary cutaneous melanoma. This is a statement of the types of population (participants in controlled clinical studies), types of interventions (and what they are compared to, even if it is no treatment), and the types of outcomes that are of interest.

Reference: Cochrane Handbook for Systematic Reviews of Interventions at www.cochrane.org/resources/handbook/index.htm