top of page


This section describes the rationale for the TwiCs approach (also known as the 'cohort multiple RCT' design), how the design is being used, the different types of published protocols relating to the design. There are also articles on theoretical and methodological aspects of the approach (including reporting guidelines) and a section comparing TwiCs and standard approaches to infrastructure and informed consent. 

Rationale for the TwiCs  approach


The theoretical article describing the design was published in 2010.


The TwiCs design was created in an attempt to overcome many of the problems associated with standard pragmatic randomised controlled trial (RCT) design (poor recruitment rates, unrepresentative trial populations, lack of long term outcomes etc); problems which reduce the generalisability of results and a sub-optimal system for efficiently informing routine healthcare decision making.

Wouters et al (2020) describe how the TwiCs approach encompasses strategies that contribute to a health care system in which “the process of generating and applying the best evidence will be natural and seamless components of the process of care itself.”

They argue that implementing innovative study designs such as TwiCs may promote scientific research in a way that is more congruous with daily care delivery, while key ethical and legal distinctions between care and research (eg, informed consent, independent ethics review) continue to exist.

Implementation of the TwiCs approach


Since its publication, the theoretical article describing the design has been well cited, and the cmRCT design is now being used in a variety of settings and arenas.

The initial partial pilot of the design was conducted in 2005-2007 in a UK NHS community clinic and the trial results were published in 2012.

A hypothetical test of the acceptability of the design was conducted in primary care mental health in the UK.

In addition to conference presentations about the design, and symposiums of triallists interested in (or already using the design), triallists in a number of different fields have cited the design as a potential way forward for research in their field eg Verkooijen 2013. And some groups have held consensus building events eg stakeholders in prostate cancer surgery

TwiCs protocols 


A growing number of protocols for studies using the TwiCs design approach are now being published in trial registries and peer reviewed online journals – below are some examples of different types of protocols.

Protocols describing the methods used to create long term observational studies (cohorts) with the facility for multiple trials



Protocols for RCTs  within already created cohorts



Protocols for RCTs  - which then build a cohort around the trial


bottom of page