A recent paper in the Journal of Clinical Epidemiology analysed the results of cluster RCTS where general practices were the unit of randomisation. Effect sizes were reported for 72 outcomes across 29 cluster RCTs. Fifteen of the 72 outcomes were significant statistically, and only one met or exceeded the alternative hypothesis (delta). Disappointingly, the authors do not classify the trials properly, as we have recommended  – with or without baseline measurements and, if baseline measurements were used, whether the study was cross-sectional or cohort. The authors seem to favour Bonferroni correction when there is more than one end-point, but this is unscientific. In situations where many study endpoints are part of a postulated causal chain, then far from ‘correcting’ for multiple observations, correspondence between different observed endpoints should reinforce a positive conclusion. Likewise, lack of correspondence should cast doubt on cause and effect conclusions. This process of triangulation between observations lies at the heart of causal thinking. The logic is laid out in more detail elsewhere. 
— Richard Lilford, CLAHRC WM Director
- Siebenhofer A, Paulitsch MA, Pregartner G, Berghold A, Jeitler K, Muth C, Engler J. Cluster-randomized controlled trials evaluating complex interventions in general practice are mostly ineffective: a systematic review. J Clin Epidemiol. 2018; 94: 85-96.
- Lamont T, Barber N, de Pury J, Fulop N, Garfield-Birkbeck S, Lilford R, Mear L, Raine R, Fitzpatrick R. New approaches to evaluating complex health and care systems. BMJ. 2016; 352: i154.
- Hemming K, Chilton PJ, Lilford RJ, Avery A, Sheikh A. Bayesian Cohort and Cross-Sectional Analyses of the PINCER Trial: A Pharmacist-Led Intervention to Reduce Medication Errors in Primary Care. PLOS ONE. 2012; 7(6): e38306.
- Lilford RJ. Beyond Logic Models. NIHR CLAHRC West Midlands News Blog. 2 September 2016.
- Watson SI, & Lilford RJ. Essay 1: Integrating multiple sources of evidence: a Bayesian perspective. In: Raine R, & Fitzpatrick R. (Eds). Challenges, solutions and future directions in the evaluation of service innovations in health care and public health. HS&DR Report No. 4.16. Southampton: NIHR Journals Library. 2016.
- Lilford RJ, Chilton PJ, Hemming K, Girling AJ, Taylor CA, Barach P. Evaluating policy and service interventions: framework to guide selection and interpretation of study end points. BMJ. 2010; 341: c4413.