Client language as a mediator of motivational interviewing efficacy: where is the evidence?

Identifying in-session indicators of client outcomes is important in determining the mechanisms of psychotherapeutic treatments, including Motivational Interviewing (MI). The current studies sought to determine if clinician behavior influences client speech, and the extent to which client speech predicted treatment outcome in clients receiving treatment for substance abuse.

Study 1 examined 38 sessions from 5 sites in Project MATCH. Sessions were coded using the Sequential Code for Process Exchanges (SCOPE) behavioral coding system. Transition probabilities and inter-rater reliability were calculated. Study 2 examined 45 sessions from the New Mexico site in Project MATCH. Sessions were coded using the MISC 1.0 behavioral coding system. Distal outcome measures were calculated for proportion of days abstinent (PDA) and drinks per drinking day (DDD). Hierarchical multiple regression and hierarchical logistic regression were used to characterize the relationship between client speech and outcome.

In Study 1, inter-rater reliability estimates indicate that coders reliably distinguished between the categories within the SCOPE. Behaviors consistent with MI (MICO) were significantly likely to be followed by client Change Talk (CT) and behaviors inconsistent with MI (MIIN) were significantly likely to be followed by Counterchange Talk (CCT). There was also a significant negative transition probability between MICO and CCT. In Study 2, CT was found to account for significant portions of outcome variability beyond that attributable to baseline measures of problem severity.

Client speech during early therapy sessions appears to be a powerful predictor of substance abuse outcome. The pattern of therapist behaviors and subsequent client language found in this data supports the intervention test in the causal chain we have described for motivational interviewing. These studies provide preliminary support for a causal chain between therapist behaviors, subsequent client speech, and drinking outcomes within motivational interviewing sessions. The results of both studies provide further support to the proposition that client speech impacts the likelihood of behavioral change, and that the occurrence of such speech is influenced by the therapist.