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External validity is also an ethical consideration in cluster-randomised trials of policy changes
  1. Karl Y Bilimoria1,
  2. Jeanette W Chung1,
  3. Larry V Hedges2
  1. 1 Department of Surgery, Feinberg School of Medicine, Surgical Outcomes and Quality Improvement Center, Northwestern University, Chicago, Illinois, USA
  2. 2 Department of Statistics, Northwestern University, Chicago, Illinois, USA
  1. Correspondence to Dr Karl Y Bilimoria, Department of Surgery, Northwestern University, Chicago, IL 60208, USA; k-bilimoria{at}

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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-randomised trial in which large cluster sizes pose unjustifiable excess risk.1 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 …

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  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Patient consent Not required.

  • Provenance and peer review Commissioned; internally peer reviewed.

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