PT - JOURNAL ARTICLE AU - Karla Hemming ED - , TI - External validity is also an ethical consideration in cluster-randomised trials of policy changes: the author’s reply AID - 10.1136/bmjqs-2018-008805 DP - 2019 Feb 01 TA - BMJ Quality & Safety PG - 168--168 VI - 28 IP - 2 4099 - http://qualitysafety.bmj.com/content/28/2/168.short 4100 - http://qualitysafety.bmj.com/content/28/2/168.full SO - BMJ Qual Saf2019 Feb 01; 28