TY - JOUR T1 - External validity is also an ethical consideration in cluster-randomised trials of policy changes JF - BMJ Quality & Safety JO - BMJ Qual Saf SP - 167 LP - 167 DO - 10.1136/bmjqs-2018-008777 VL - 28 IS - 2 AU - Karl Y Bilimoria AU - Jeanette W Chung AU - Larry V Hedges Y1 - 2019/02/01 UR - http://qualitysafety.bmj.com/content/28/2/167.abstract N2 - 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 … ER -