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Ethical implications of excessive cluster sizes in cluster randomised trials
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  • Published on:
    External Validity Is Also an Ethical Consideration in Cluster-Randomized Trials of Policy Changes
    • Karl Y. Bilimoria, John Benjamin Murphy Professor of Surgery Surgical Outcomes and Quality Improvement Center, Department of Surgery, Feinberg School of Medicine, Northwestern University
    • Other Contributors:
      • Jeanette W. Chung, Research Associate Professor
      • Larry V. Hedges, Board of Trustees Professor of Statistics and Education and Social Policy

    Hemming et al. (“Ethical Implications of Excessive Cluster Sizes in Cluster Randomized Trials,” 20 February 2018) cite the FIRST Trial as an example of a “higher risk” cluster-randomized trial in which large cluster sizes pose unjustifiable excess risk. The authors state, “[t]he obvious way to reduce the cluster size in this study is to reduce the duration of the trial…”

    We believe this to be an inappropriate recommendation stemming from an inaccurate appraisal of the FIRST Trial.

    The FIRST Trial was designed to inform a potential policy change in U.S. resident duty hours. In the Statistical Analysis Plan, which was made available at, we clearly and prospectively stated that “[t]his study is a trial-based evaluation of potential policy effects on patient safety and resident wellbeing... this study is intended to inform real-world policy decision-making with respect to resident duty hours regulation.”[1] The SAP and Supplemental Appendix ( also provides all assumptions for our power calculations and cluster sizes, which were not large in the case of resident outcomes.[2]

    As such, it was important that the trial closely resemble real-world conditions in which residency training occurs and duty hour policies are implemented. A shorter study would pose risks owing to non-standard, multiple policy shifts and would increase administrative/organizational bu...

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    Conflict of Interest:
    None declared.