A Multivariate Meta-Analysis of Motivational Interviewing Process and Outcome
Motivational interviewing (MI) theory proposes a process whereby a set of therapist behaviors has direct effects on client outcomes and indirect effects through in-session processes (e.g., client change talk). Despite clear empirical support for the efficacy of MI across settings, the results of studies evaluating proposed links between MI process and outcome have been less clear. In the present study, we used a series of multivariate meta-analyses to test whether there are differential relationships between specific MI-consistent and MI-inconsistent therapist behaviors, MI therapist global ratings, client change language, and clinical outcomes. Based on 19 primary studies (N = 2,614), we found a significant relationship between MI-consistent therapist behaviors and greater client change talk, as well as greater client sustain talk. Higher therapist global ratings (empathy and MI spirit) were significantly related to increased MI-consistent behaviors, decreased MI-inconsistent behaviors, increased client change talk, yet also increased client sustain talk. Therapist global ratings were not significantly related to clinical outcomes. Client sustain talk was a significant predictor of worse clinical outcomes, while client change talk was unrelated to outcome. Variability within the correlations indicated that MI-consistent and MI-inconsistent therapist behaviors were differentially related to therapist global ratings of empathy and MI spirit. Similar to past research, present findings provide equivocal support for hypothesized MI process outcome relationships. Clinical implications and future areas of MI mechanism research are discussed.