Process research in understanding and applying psychological therapies

Objectives. Research on the process of psychological therapy aims to demonstrate how therapy works, partly to increase understanding, but primarily to increase effectiveness by pointing to the crucial ingredients which effect change. This paper aims to demonstrate some of the reasons why process research should be undertaken in the attempt to increase therapeutic effectiveness. Methods. A model of scientific inquiry suggests three broad types of process research: (1) studies which describe behaviours and processes occurring within therapy sessions (exploratory studies); (2) studies which investigate the links between specific psychotherapy processes and treatment outcome (hypothesis testing); (3) studies which examine the links between specific psychotherapy processes and theories of change (theory development). Using this typology, we describe key aspects of process research: what it is; what has been studied; the limitations of existing research. Results. Descriptive studies have deepened understanding of the therapeutic process; however, a large number of reliable process‐outcome links have been hard to establish. Comparative studies have been rare. Studies which are linked to models of change and which attempt to track therapist responsiveness are more complex and have been more promising. Most studies are beset by methodological difficulties. Conclusions. There are a number of promising future research possibilities and methods. Despite methodological challenges, the field is developing and research is encouraging. We argue that process research has a significant place in advancing our understanding of the complexity of therapeutic change, and hence in facilitating theory development and effective therapeutic interventions.