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Review of an innovative approach to practical trials: the ‘cohort multiple RCT’ design


The ‘cohort multiple randomised controlled trial’ (cmRCT) is an innovative approach to the design and conduct of RCTs which compare the effectiveness of interventions to usual care (Relton et al, 2010). The design utilises a large long term observational cohort of people with the condition of interest, regularly measuring the outcomes of the whole cohort. The cohort in the cmRCT design allows multiple trial populations to be quickly identified and recruited and interventions tested against usual care. Information consent processes are similar to those in routine healthcare.


Studies using the design were identified through citations of the original theoretical article (Relton et al 2010). Data were extracted from published articles, study protocols and presentations.


16 studies implementing the cmRCT design were identified with a total of 18 ongoing or completed trials were embedded within these cohorts. Some cohorts focussed on a single disease or injury (e.g. hip fracture, breast cancer, colorectal cancer), others had a wider focus (e.g. risk of mental health conditions, risk of falls). Some studies built a cohort around a trial, and then obtained further funds to exploit the cohort for further trials within that cohort.


This review of the cmRCT design in practice provides examples of the design in the UK, Canada and the Netherlands and will help guide researchers interested in using the cmRCT design. Future research needs to assess the acceptability and efficiency of this approach, i.e., if/when this design is preferable to the standard approach to single separate RCTs.

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This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver ( applies to the data made available in this article, unless otherwise stated.

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Relton, C., Thomas, K., Nicholl, J. et al. Review of an innovative approach to practical trials: the ‘cohort multiple RCT’ design. Trials 16 (Suppl 2), P114 (2015).

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