Practice based evidence and the law of variability in psicological treatment

Variability is intrinsic to all human activities and psychotherapy is no exception. However, trials methodology is not suited to investigating and building our knowledge about variability. By contrast, the paradigm of practice-based evidence, which focuses on routine practice, is a better way of researching the phenomenon of variability. We outline the key hallmarks of a practice-based evidence paradigm and report on a series of UK studies drawing on datasets using the Clinical Outcomes in Routine Evaluation (CORE) measures and also datasets from the UK Improving Access to Psychological Therapies (IAPT) initiative. We consider variability at the level of psychological treatment models, at patient, therapist and group levels, as well as at service levels, and finally at the level of neighborhoods and regions. We conclude that variability occurs at all levels of psychological therapies and that equal investment is required at these levels similar to that of trials in order to develop large, national, standardized practice-based datasets in order to advance our understanding of variability in the psychological therapies.