Trials within cohorts (TwiCs): A novel design to efficiently embed pragmatic randomised trials into cohort studies

Trials within cohorts (TwiCs) is a novel trial design that promises to overcome frequent challenges of traditional randomised clinical trials, such as high cost, slow recruitment, and a limited generalisability of results. In studies with a TwiCs approach, a randomised comparison is nested into an observational cohort by design in order to use synergies in infrastructure for recruitment and data collection. The TwiCs design has been applied to the assessment of interventions in different medical fields in several countries using three different consent patterns. In Switzerland, the Swiss HIV Cohort Study is taking a pioneering role as the first cohort in the country to implement the TwiCs design.