LUCID Workshops

Optimising interventions using trial designs – introducing MOST and factorial designs

Rebecca Walwyn & Sam Smith

Background, aims and content

What is the context to the workshop, what will it cover, what will participants gain from attending?

Typically, complex interventions are developed, piloted and then evaluated in a parallel-group trial. This treats complex interventions as black-boxes, where randomised evidence is built only on which packages are superior to other packages, not on the contributions of the components. It is also hugely inefficient.

Since 2005, there has been a growing literature in the US on using factorial designs to explore and confirm the individual and combined effects of the components of complex healthcare interventions. This literature in turn builds on an established Design of Experiments literature.

We will provide an overview of the rationale for, and literature on, using factorial trial designs to empirically optimise complex interventions, introducing the Multiphase Optimisation Strategy (MOST) of Collins et al. We will then focus on practical case studies to illustrate the issues that need to be considered when adopting this approach. Finally, we will address the common concerns in a question and answer session.

Participants will gain an understanding of why optimisation is an important stage in developing and evaluating complex interventions and an appreciation of the practical considerations involved.

Target Group

(Attendees assumed to have a basic knowledge of or interest in intervention development, but may have no prior knowledge of the workshop topic)

Intervention developers

Clinical investigators


Health economists

Trial Managers