Motivational interviewing technical process and moderated relational process with underage young adult heavy drinkers.

This study tested technical and relational processes hypothesized to explain the therapeutic benefit of an efficacious brief motivational interview (BMI). A randomized controlled trial compared the efficacy of a BMI to an attention-matched control (i.e., relaxation training [REL]) for reducing heavy alcohol consumption and associated negative consequences. Participants were underage, past-month heavy drinkers recruited from community settings (N = 167; ages 17-20; 62% female; 59% White). Data were collected on session recordings, using established motivational interviewing process measures. Statistical analyses followed 3 steps. First, a latent class model determined the optimal class solution for characterizing proportion change talk means within BMI and REL. Next, the probability of proportion change talk class membership was examined as a mediator and then as a moderated mediator of BMI efficacy. The latent class model yielded a 3-class solution, including a low-increasing proportion change talk class (n = 61), a moderate-increasing proportion change talk class (n = 97), and a nonlinear proportion change talk class (n = 7). Across the outcomes examined, membership in the moderate-increasing class rather than the low-increasing class mediated BMI effects on alcohol-related consequences at 6 weeks. Mediation tests for consequences at 3 months and heavy drinking were nonsignificant. Moderated mediation results for therapist empathy and MI Spirit were nonsignificant. Findings suggest that moderate increases in prochange statements, relative to anti- or neutral-change statements, help explain BMI effects on reducing alcohol-related negative consequences soon after intervention. (PsycINFO Database Record (c) 2019 APA, all rights reserved).