TY - JOUR T1 - External validity is also an ethical consideration in cluster-randomised trials of policy changes: the author’s reply JF - BMJ Quality & Safety JO - BMJ Qual Saf SP - 168 LP - 168 DO - 10.1136/bmjqs-2018-008805 VL - 28 IS - 2 AU - Karla Hemming A2 - , Y1 - 2019/02/01 UR - http://qualitysafety.bmj.com/content/28/2/168.abstract N2 - We would like to thank the authors of the FIRST trial for responding to our paper on ‘Ethical implications of excessive cluster sizes in cluster randomised trials’.1 We are pleased that our paper has generated this interest. The science and methodology of trial design are constantly evolving and will evolve faster, to the future benefit of science, if we can … ER -