A1196
Title: Orthogonal factorial designs for trials of therapist-delivered interventions
Authors: Rebecca Walwyn - University of Leeds (United Kingdom) [presenting]
Rosemary Bailey - University of St Andrews and Queen Mary University of London (United Kingdom)
Arpan Singh - University of Leeds (United Kingdom)
Neil Corrigan - University of Leeds (United Kingdom)
Steven Gilmour - KCL (United Kingdom)
Abstract: It is recognised that treatment-related clustering should be allowed for in the sample size and analyses of individually-randomised parallel-group trials evaluating therapist-delivered interventions such as psychotherapy. Interventions are a treatment factor, but therapists are not. If the aim of a trial is to separate effects of therapists from those of interventions, interventions and therapists are regarded as two potentially interacting treatment factors (one fixed, one random) with a factorial structure. The specific design is considered where each therapist delivers each intervention (crossed therapist-intervention design), and the resulting therapist-intervention combinations are randomised to patients. A classical design of experiments approach is adopted to propose a family of orthogonal factorial designs and their associated data analyses, which also allow for therapist learning and centre. The associated data analyses are set out using ANOVA and regression and report the results of a small simulation study that was conducted to explore the performance of the proposed randomization methods on estimating the intervention effect, the between-therapist variance, and the between-therapist variance in the intervention effect. It is concluded that a more purposeful trial design has the potential to lead to better evidence on a range of complex healthcare interventions and outline areas for further methodological research.
