Serial mediation analysis of treatment-specific processes in two contrasting alcohol treatments

Introduction: This study explored whether treatment-specific processes linking therapist behaviors, post-session client ratings, and 3-month proximal outcomes (i.e., end of treatment) can explain 12-month outcomes for two contrasting alcohol treatment conditions with equivalent overall outcomes.Methods: This study is a secondary analysis of the UK Alcohol Treatment Trial (UKATT), a multi-center ran-domized controlled trial of treatment for alcohol problems comparing 3-session motivational enhancement therapy (MET) to 8-session social behaviour and network therapy (SBNT). Among 742 adult clients included in UKATT, 351 had one treatment session recorded and coded and were followed-up 3 and 12 months after baseline. The study team conducted serial mediation analyses to test whether the frequency and quality of MET and SBNT skills were related to 12-month alcohol outcomes (drinks per drinking day) through postsession client ratings of treatment progress (Processes of Change Questionnaire, PCQ), readiness to change (RTC) and social support for drinking after 3-months.Results: Higher quality of MET skills was related to higher PCQ scores, which were in turn related to greater post-treatment RTC, and subsequently to better alcohol outcomes. Total indirect effect was consistently significant. In contrast, only PCQ was predictive of treatment outcome in the SBNT portion of the model.Conclusions: This study provides evidence from a large pragmatic trial that the quality of MET skills positively influences alcohol outcomes in part through improvements in motivation during treatment and actively trying to change when treatment ends. Research should explore the ways in which SBNT secured outcomes that were equivalent to MET.