This module will discuss differences between studies. We learn how to recognize and deal with differences between studies in a review. Some statistical methods such as random effects meta-analysis, subgroup analysis and meta-regression can help address these differences, and this module will explain these techniques.

Learning objectives

• Understand that studies usually differ both clinically and methodologically
• Appreciate that differences between studies can result in (statistical) heterogeneity - differences in their results
• Be able to identify heterogeneity
• Know some strategies for dealing with heterogeneity
• Understand the difference between fixed effect and random effects meta-analysis
• Understand when to use subgroup analyses
• Be aware of meta-regression as a tool for exploring differences between studies

Relevant sections of the Reviewers' Handbook

• Section 8

Where does this go in a Cochrane review?

• In the protocol where you will need to specify factors that you are planning to investigate as potential causes of heterogeneity
• The Methods section of the review should detail what you have done to identify or examine heterogeneity. It is especially important to tell the reader which analyses were pre-specified and which were 'post hoc', i.e. designed after collecting all the studies for your review
• The Results section should present results of subgroup analyses and meta-regressions (if used). Remember to interpret the results with caution, and keep in mind the possibility that findings may be spurious if you do more than very few analyses