A meta-analysis of motivational interviewing across behavioral domains

Motivational Interviewing (MI) is a client centered, directive therapeutic method designed to enhance motivation for change by helping individuals to explore and resolve ambivalence. MI utilizes signals of readiness to match treatment strategies to individuals' current level of motivation in an attempt to reduce resistance and counterarguments against change. The evidence base for MI is rapidly growing and to date two meta-analyses have been conducted on this topic. The current meta-analysis is an update to previous meta-analyses and includes 85 clinical trials across nine problem areas. Between-group effect sizes were calculated for 586 variables, representing 19,708 participants. The overall combined effect size for all studies of MI was .41. Effect sizes were largest for studies of diet and exercise and smallest among smoking studies. Changes in effect size across time were inconsistent. Observed effect sizes were higher among Black samples. Training and treatment fidelity information revealed highly variable practices across studies. The meta-analysis points to the need for knowledge regarding the mediators and moderators of MI efficacy and increased research on training standards. (PsycINFO Database Record (c) 2010 APA, all rights reserved)