Defining the criteria for including studies and how they will be grouped for the synthesis

Joanne E. McKenzie, Sue E. Brennan, Rebecca E. Ryan, Hilary J. Thomson, R.V. Johnson, James Thomas

Research output: Chapter in Book/Report/Conference proceedingChapter (Book)Researchpeer-review


Key Points:
- The scope of a review is defined by the types of population (participants), types of interventions (and comparisons), and the types of outcomes that are of interest. The acronym PICO (population, interventions, comparators and outcomes) helps to serve as a reminder of these.
- The population, intervention and comparison components of the question, with the additional specification of types of study that will be included, form the basis of the pre-specified eligibility criteria for the review. It is rare to use outcomes as eligibility criteria: studies should be included irrespective of whether they report outcome data, but may legitimately be excluded if they do not measure outcomes of interest, or if they explicitly aim to prevent a particular outcome.
- Cochrane Reviews should include all outcomes that are likely to be meaningful and not include trivial outcomes. Critical and important outcomes should be limited in number and include adverse as well as beneficial outcomes.
- Review authors should plan at the protocol stage how the different populations, interventions, outcomes and study designs within the scope of the review will be grouped for analysis.
Original languageEnglish
Title of host publicationCochrane Handbook for Systematic Reviews of Interventions
EditorsJulian P.T. Higgins, James Thomas, Jacqueline Chandler, Miranda Cumpston, Tianjing Li, Vivian A. Welch, Matthew J. Page
Place of PublicationChichester UK
PublisherJohn Wiley & Sons
Number of pages34
ISBN (Electronic)9781119536611
ISBN (Print)9781119536628
Publication statusPublished - 5 Oct 2019


  • systematic review
  • evidence synthesis
  • Evidence review
  • Research methodology

Cite this

McKenzie, J. E., Brennan, S. E., Ryan, R. E., Thomson, H. J., Johnson, R. V., & Thomas, J. (2019). Defining the criteria for including studies and how they will be grouped for the synthesis. In J. P. T. Higgins, J. Thomas, J. Chandler, M. Cumpston, T. Li, V. A. Welch, & M. J. Page (Eds.), Cochrane Handbook for Systematic Reviews of Interventions (2nd ed., pp. 33–66). John Wiley & Sons.