Motivational interviewing: A meta-analysis of controlled clinical trials

Abstract

This is a meta-analytic review of controlled clinical trials investigating adaptations of motivational interviewing (AMIs), a promising approach to treating problem behaviors. For each study, descriptive characteristics were coded and individual effect sizes (Cohen's d) were computed. In order to evaluate comparative efficacy, combined effect sizes for AMIs were calculated, separated by comparison group and problem area. To test for sustained efficacy, post-treatment & follow-up effect sizes for AMIs were compared. Additional data were compiled to evaluate the clinical impact of AMIs. Finally, potential moderators were analyzed to test five specific hypotheses related to the effects of AMIs. Thirty clinical trials were included in this review, representing a wide variety of studies. AMIs were equivalent to other active treatments and yielded moderate effects (ranging from .25 to .57) compared to no-treatment or placebo controls for problems involving alcohol, drugs, and diet & exercise. These effects were sustained through an average of 67 weeks of follow-up and for as long as 4 years post-treatment. Based on four studies, there was weak evidence for AMIs in the areas of smoking cessation and HIV-risk behaviors. Overall, AMIs demonstrated considerable clinical impact, with 51% improvement rates, a mean within-group effect size of .82, a 56% reduction in client drinking, and moderate effects on social impact measures (d = .47) such as days of work lost due to substance use. Each of the five specific hypotheses in this meta-analysis was at least partially confirmed. Miller's lab (the founder of motivational interviewing) produced the best outcomes for AMIs, while AMI treatments were most efficacious for severe client samples. AMIs generated the best results when used as preludes to further clinical services rather than as stand-alone treatments. Studies of low methodological quality yielded better outcomes for AMIs than did high quality studies, although the overall picture with regards to quality was unclear. Finally. AMIs showed a significant dose-effect relationship, with higher treatment doses resulting in better study outcomes. Additional analyses provided evidence that the conclusions of this meta-analysis are reasonably immune to the effects of client attrition as well as to publication bias.