Exploratory trials in mental health: anything to learn from other disciplines?

Confirmatory randomised controlled trials require solid justifications, especially with regard to whether the experimental intervention is promising. Such evidence is generated in exploratory trials. However, empirical evidence shows that the quality of such trials is still suboptimal. More generally, the development process of healthcare interventions and especially of drugs, remains inefficient. Over the past 10-20 years, a vast amount of methodological work has been published about exploratory trials. This overview introduces some of the concepts and recent developments in the field.

A narrative approach was taken for this overview. This article focuses on study designs developed outside the mental health field to introduce concepts that might not be familiar to clinical researchers in psychiatry and psychology. Non-randomised and randomised exploratory trial designs are covered. The article ends with a brief discussion on pilot studies and their difference to exploratory studies.

Classical designs for exploratory trials such as Simon's two-stage design still have a role. However, randomised exploratory trials are probably more suitable for mental health interventions. Newer, more flexible designs such as multistage, multiarm trials or platform trials have the potential to improve the efficiency of exploratory and subsequently confirmatory experiments.

Although often not directly applicable, borrowing (study) design ideas from other medical disciplines has the potential to improve exploratory trials in the mental health field. At the same time, more explicit use of study designs specifically designed for exploratory trials will help to improve the transparency of such trials.