Evaluating therapist adherence in motivational interviewing by comparing performance with standardized and real patients

Objective: The goal of measuring therapist adherence is to determine whether a therapist can perform a given treatment. Yet, the evaluation of therapist behaviors in most clinical trials is limited. Typically, randomized trials have few therapists and minimize therapist variability through training and supervision. Furthermore, therapist adherence is confounded with uncontrolled differences in patients across therapists. Consequently, the extent to which adherence measures capture differences in actual therapist adherence versus other sources of variance is unclear.

Method: We estimated intra-class correlations (ICCs) for therapist adherence in sessions with real and standardized patients (RPs and SPs), using ratings from a motivational interviewing (MI) dissemination trial (Baer et al., 2009) in which 189 therapists recorded 826 sessions with both patient types. We also examined the correlations of therapist adherence between SP and RP sessions, and the reliability of therapist level adherence scores with generalizability coefficients (GCs).

Results: ICCs for therapist adherence were generally large (average ICC for SPs = .44; average ICC for RPs = .40), meaning that a given therapist's adherence scores were quite similar across sessions. Both ICCs and GCs were larger for SP sessions compared to RPs on global measures of MI adherence, such as Empathy and MI Spirit. Correlations between therapist adherence with real and standardized patients were moderate to large on 3 of 5 adherence measures.

Conclusion: Differences in therapist-level adherence ratings were substantial, and standardized patients have promise as tools to evaluate therapist behavior.