Welcome to the TwiCs network where we share information about the Trials within Cohorts (TwiCs) approach for designing and conducting practical randomised controlled trials.

Trials within Cohorts (TwiCs) approach uses infrastructures (cohorts) to facilitate the conduct of multiple randomised controlled trials.


See COVIDENCE for a recent example of this approach to tackle questions related to the management of COVID-19 in the UK.


The design

The term 'TwiCs' was coined at the first symposium on the 'cohort multiple RCT' design. This approach to trial design (the cmRCT design) was first described in the BMJ in 2010 article in the context of healthcare.

Key features of the cmRCT design are:

  • A large observational cohort of people with the condition

  • Repeated measurement of outcomes for the whole cohort

  • Capacity for multiple randomised controlled trials over time

  • Patient-centred informed consent


The advantages of the design are that the cohort serves as a representative pool from which eligible people can be selected and approached for trial participation. This provides a platform for testing multiple interventions.

The standard approach to informed consent is the 'everything up front' approach. The TwiCs approach advocates the use of a patient-centred approach to informed consent procedure - one which is more similar to how information is provided in healthcare settings where information is staged in order to maximise relevance for the patient.

More than 80 studies have or are using the design. Researchers in the UK, Canada, USA, France, Netherlands, Finland, and Australia;  are use the TwiCs design approach to help address questions in a variety of fields (breast cancer, bone metastases, rectal cancer, mental health, care of the elderly, rare diseases, etc).  The design is now being used to trial both medicinal products (CTIMPs) and non-medicinal products.


Though originating in healthcare, the TwiCs approach to trial design can be used to inform decision making in any area, e.g. education, social care, crime, energy use.


This website describes key features of the TwiCs approach and links to articles describing the methodologies, and examples of use of the TwiCs approach in hospital settings and primary care/ population based settings.

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Supported by a Wellcome Trust grant and the NIHR CLAHRC for Yorkshire & Humber