An adaptive method for assigning clinical trials wait-times for controls.

Wait-list control clinical trials are popular among psychologists and rehabilitation specialists partly because all participants receive the intervention. In 2 arm wait-list control trials, individuals randomized to the treatment group receive immediate treatment whereas individuals randomized to the control group wait a fixed amount of time before intervention is initiated. For interventions that have varying durations, careful consideration must be given to the period that participants in the control group have a delay until treatment begins, as incongruent wait times compared to the intervention durations of the treatment group may introduce confounding into the evaluation of the treatment differences. To alleviate this issue, we propose to adaptively assign wait times to individuals randomized to the control group based on the intervention duration of those in the treatment group. Simulations demonstrate the that our method not only results in similar timing distributions between participants in the treatment and control groups, but also allows participants in the control group to initiate treatment earlier than the traditional design. The latter characteristic may reduce dropout and result in more efficient study enrollment.