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Summaries of Two Meta-Analyses of Motivational Interviewing Published in 2005 

Hettema, J., Steele, J., & Miller, W. R.  (2005) Motivational Interviewing. Annual Review of Clinical Psychology, 1: 91-111.

This meta-analysis of 72 clinical trials spanned a range of target behaviors.  Short-term between-group effect size of MI was 0.77.  At one year follow-up, the effect size decreased to 0.30.  Effect sizes of MI were larger with ethnic minority populations.  Manual-guided practice may have decreased effect size, possibly because it allowed a less client-centered style.  There is high variability of effectiveness across MI providers, populations, target problems and settings. 

Rubak, S, Sandboek, A., Lauritzen, T., & Christensen, B. (2005). Motivational interviewing: a systematic review and meta-analysis. British Journal of General Practice, 55: 305-312.

In this second meta-analysis, 72 randomized controlled trials were also included.   Here the meta-analysis showed a significant effect (95% confidence interval) for MI for combined effect estimates for body mass index, total blood cholesterol, systolic blood pressure, blood alcohol concentration and standard ethanol content, while combined effect estimates for cigarettes per day and for HbA1c were not significant. MI had a significant and clinically relevant effect in approximately three out of four studies, with an equal effect on physiological (72%) and psychological (75%) target problems. Psychologists and physicians obtained an effect in approximately 80% of the studies, while other healthcare providers obtained an effect in 46% of the studies. When MI is used in brief encounters of 15 minutes, 64% of the studies showed an effect. More than one encounter with the patient ensures the effectiveness of MI.  MI in a scientific setting outperforms traditional advice giving in the treatment of a broad range of behavioral problems and diseases.

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