Predictors of engagement with between-session work in Cognitive Behavioural Therapy (CBT)-based interventions: a mixed-methods systematic review and "best fit" framework synthesis.

Between-session work (BSW) acts as the vehicle to translate skills learnt in therapy sessions into adaptive changes in everyday life, a key goal in Cognitive Behavioural Therapies (CBT). Despite a well-established relationship between engagement with BSW and enhanced treatment outcomes, difficulties completing between-session tasks are common and factors affecting patient engagement with BSW are poorly understood. This mixed-methods systematic review and "best fit" framework synthesis explored predictors of engagement with BSW in CBT-based interventions. Comprehensive searches were conducted across five databases, identifying 59 eligible studies. This combined theory and empirical evidence approach depicted ten predictor themes related to between-session engagement, spanning individual, relational and contextual concepts. While ambiguous findings were generated by existing evidence, several factors emerged as relatively consistent predictors of engagement with BSW: positive patient beliefs regarding BSW and treatment such as perceived helpfulness, and practitioner competency in planning and reviewing BSW, including providing a rationale and addressing difficulties were associated with greater engagement. Conversely, patient in-session resistance, including counter change talk, was an indicator of disengagement between-sessions. The impact of patient symptomology, sociocultural environment, practitioner beliefs and the therapeutic relationship is unclear. The conceptual model presented offers a testable framework for researchers and a guideline for practitioners.