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Q: Whats the difference between Registry-based randomised clinical trials and the cmRCT/ TwiCs design?

A: Registry-based randomised trials use a large inclusive clinical registry with unselected consecutive enrolment and combine this with a prospective randomised controlled trial.

Similarities between the cmRCT and the RRCT 

- both utilise a large group (cohort/ register) of people with the condition(s) of interest to identify those who may be eligible for the trial.

- both have the potential to facilitate the operation of multiple trials within that group (cohort/ registry)

Differences between the cmRCT and RRCT

- the RRCT uses a standard approach to informed consent - where the clinician tells people about treatments that they may or may not be randomised to, whereas the cmRCT uses 'patient centred informed consent' (key feature 7). This means that for each trial, those people in the cohort who are eligible for the trial are randomised first, then those randomised to the new intervention are informed retrospectivly that they have been randomly selected to try this intervention. Those in the control arm (where the status quo is unchanged) are not told about interventions/ treatments that they have not/ will not be offered. In this way the processes of informed consent are a similar as possible to those in routine care - where patients are not told about treatments that they are not then offered, nor are they told that their treatment allocation will be decided by chance.

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