Including variants on randomized trials

Julian P.T. Higgins, Sandra Eldridge, Tianjing Li

Research output: Chapter in Book/Report/Conference proceedingChapter

16 Scopus citations


In cluster-randomized trials, groups of individuals rather than individuals are randomized to different interventions. For the purposes of an assessment of risk of bias using the RoB 2 tool, this chapter defines participants in cluster-randomized trials as those on whom investigators seek to measure the outcome of interest. Parallel-group trials allocate each participant to a single intervention for comparison with one or more alternative interventions. In contrast, crossover trials allocate each participant to a sequence of interventions. Crossover trials are suitable for evaluating interventions with a temporary effect in the treatment of stable, chronic conditions. To include a study with more than two intervention groups in a meta-analysis, a recommended approach is to omit groups that are not relevant to the comparison being made, and to combine multiple groups that are eligible as the experimental or comparator intervention to create a single pair-wise comparison. Alternatively, multi-arm studies are dealt with appropriately by network meta-analysis.

Original languageEnglish (US)
Title of host publicationCochrane Handbook for Systematic Reviews of Interventions
Number of pages25
ISBN (Electronic)9781119536604
ISBN (Print)9781119536628
StatePublished - Jan 1 2019


  • Cluster-randomized trials
  • Crossover trials
  • Intervention groups
  • Multi-arm studies
  • Network meta-analysis
  • Risk of bias assessment tool
  • RoB 2 tool

ASJC Scopus subject areas

  • General Medicine


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