Parsing within & between-person dynamics of therapy homework completion and clinical symptoms in two cognitive behavioral treatments for adults with anhedonia.

OBJECTIVE: Homework is a key theoretical component of cognitive-behavioral therapies, however, the effects of homework on clinical outcomes have largely been evaluated between-persons rather than within-persons. METHODS: The effects of homework completion on treatment response were examined in a randomized trial comparing Behavioral Activation Treatment for Anhedonia (BATA, n = 38), a novel psychotherapy, to Mindfulness-Based Cognitive Therapy (MBCT, n=35). The primary endpoint was consummatory reward sensitivity, measured weekly by the Snaith Hamilton Pleasure Scale (SHAPS), up to 15 weeks. Multilevel models evaluated change in SHAPS scores over time and the effects of clinician-reported and participant-reported homework. RESULTS: BATA and MBCT resulted in significant, equivalent reductions in SHAPS scores. Unexpectedly, participants who completed greater mean total amounts of homework did not improve at a faster rate (i.e., no between-person effect). However, sessions with greater than average participant-reported homework completion were associated with greater than average reductions in SHAPS scores (i.e., a within-person effect). For clinician-reported homework, this effect was only evident within the BATA condition. CONCLUSION: This study shows psychotherapy homework completion relates to symptomatic improvement in cognitive-behavioral treatments for anhedonia when session-to-session changes are examined within-person. On the contrary, we found no evidence that total homework completion predicted greater improvements between-person. When possible, psychotherapy researchers should evaluate their constructs of interest across multiple sessions (not just pre/post) to allow more direct tests of hypotheses predicted by theoretical models of individual change processes.