The technical hypothesis of motivational interviewing: a meta-analysis of MI's key causal model

Abstract

Objective: The technical hypothesis of motivational interviewing (MI) posits that therapist-implemented MI skills are related to client speech regarding behavior change and that client speech predicts client outcome. The current meta-analysis is the first aggregate test of this proposed causal model.

Method: A systematic literature review, using stringent inclusion criteria, identified 16 reports describing 12 primary studies. We used review methods to calculate the inverse-variance-weighted pooled correlation coefficient for the therapist-to-client and the client-to-outcome paths across multiple targeted behaviors (i.e., alcohol or illicit drug use, other addictive behaviors).

Results: Therapist MI-consistent skills were correlated with more client language in favor of behavior change (i.e., change talk; r = .26, p < .0001), but not less client language against behavior change (i.e., sustain talk; r = .10, p = .09). MI-inconsistent skills were associated with less change talk (r = -.17, p = .001) as well as more sustain talk (r = .07, p = .009). Among these studies, client change talk was not associated with follow-up outcome (r = .06, p = .41), but sustain talk was associated with worse outcome (r = -.24, p = .001). In addition, studies examining composite client language (e.g., an average of negative and positive statements) showed an overall positive relationship with client behavior change (r = .12, p = .006; k = 6).

Conclusions: This meta-analysis provides an initial test and partial support for a key causal model of MI efficacy. Recommendations for MI practitioners, clinical supervisors, and process researchers are provided.

Conflict of interest statement

There are no conflicts of interest associated with this manuscript.

Figures

Figure 1

Flow of primary study inclusion Notes. K/k is defined as number of groups. aGlynn & Moyers, 2010; Morgenstern et al, 2013. bDeappen et al., 2010; Strang & McCambridge, 2004. cKarno et al., 2010; Moyers et al., 2007; Walker et al., 2011. dc path studies examined the effect of MI-Consistent or Inconsistent Skills on patient outcome (Gaume et al., 2009; McCambridge et al., 2011; Tollison et al., 2008/2010). eThese studies examined the effect of MI training on technical skill acquisition. fApodaca et al., 2013; Miller et al., 1993; Morgenstern et al., 2013. A total of 16 published reports tested the a and/or b paths for 12 clinical trials.

Figure 2

Meta-analytic results on the Technical Hypothesis of MI efficacy Notes. *** p < .001; ** p < .005; * p < .05 †p < .10.