Metanalysis

Hettema, J.E., Steele, J.M., Miller, W.R. (2005). Motivational Interviewing. Annual Review of Clinical Psychology, 1, 91-111.
Full text: http://www.jennyhettema.com/annurev.clinpsy.1.pdf

Rubak, S, Sandboek, A., Lauritzen, T., & Christensen, B. (2005). Motivational interviewing: a systematic review and meta-analysis. British Journal of General Practice, 55: 513, pp. 305-312.
Full text: http://motivationalinterview.org/library/RubakMIreview.pdf

Lundahl, B.W., Kunz, C., Brownell, C., Tollefson, D., Burke, B.L. (2010) A Meta-Analysis of Motivational Interviewing: Twenty-Five Years of Empirical Studies, Research on Social Work Practice, 20 (2), 137-160