External validity is also an ethical consideration in cluster-randomised trials of policy changes

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 US resident duty hours. In the Statistical Analysis Plan (SAP), which was made available at www.nejm.org, we clearly and prospectively stated, '[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.'2 The...

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