Best (but oft-forgotten) practices: Designing, analyzing, and reporting cluster randomized controlled trials

Andrew W. Brown, Peng Li, Michelle M Bohan Brown, Kathryn A. Kaiser, Scott W. Keith, J. Michael Oakes, David B. Allison

Research output: Contribution to journalReview articlepeer-review

59 Scopus citations


Cluster randomized controlled trials (cRCTs; also known as group randomized trials and community-randomized trials) are multilevel experiments in which units that are randomly assigned to experimental conditions are sets of grouped individuals, whereas outcomes are recorded at the individual level. In human cRCTs, clusters that are randomly assigned are typically families, classrooms, schools, worksites, or counties. With growing interest in community-based, public health, and policy interventions to reduce obesity or improve nutrition, the use of cRCTs has increased. Errors in the design, analysis, and interpretation of cRCTs are unfortunately all too common. This situation seems to stem in part from investigator confusion about how the unit of randomization affects causal inferences and the statistical procedures required for the valid estimation and testing of effects. In this article, we provide a brief introduction and overview of the importance of cRCTs and highlight and explain important considerations for the design, analysis, and reporting of cRCTs by using published examples.

Original languageEnglish (US)
Pages (from-to)241-248
Number of pages8
JournalAmerican Journal of Clinical Nutrition
Issue number2
StatePublished - Aug 1 2015

Bibliographical note

Funding Information:
We thank John A Dawson for his input and feedback. The authors’ responsibilities were as follows—all authors: contributed to the content of the article, critical review of the content, editing of drafts, and approval of final draft. The opinions in this article are those of the authors and not necessarily those of the NIH or any other organization. None of the authors reported a conflict of interest.


  • Community randomized trial
  • Group randomized trial
  • Intraclass correlation coefficient
  • Power analysis
  • Reporting fidelity


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