Enhancing brief motivational interventions for substance use: examining the influence of affirmation and self-efficacy strategies on drug use outcomes in primary care
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INTRODUCTION: While research indicates that Motivational Interviewing (MI) is effective for reducing substance use, little is known about whether brief MI-based interventions reduce drug use in a primary care setting, or what processes impact outcomes. Mixed findings in MI process studies have led investigators to call for research exploring alternative process variables that may predict outcomes. The current study is a secondary data analysis using coded audio-recordings from a randomized controlled trial that tested the efficacy of two brief MI-based interventions as part of the `Assessing Screening Plus brief Intervention's Resulting Efficacy to stop drug use' (ASPIRE) trial. It was hypothesized that skill in affirming clients and enhancing self-efficacy (also assessed as a composite self-enhancement variable) would be associated with lower frequency of drug use at 6 weeks and 6 months after controlling for baseline drug use and indicators of general MI proficiency. METHODS: Audio-recordings from two intervention conditions [Enhanced Motivational Intervention (EMI; N=176) and Brief Negotiated Interview (BNI; N=174)] were coded with behavior counts and global interventionist skill ratings using an established coding system for MI and a study-specific coding manual. A series of negative binomial regression models were conducted that were stratified by intervention due to the different goals and characteristics of the two interventions. Secondary and tertiary analyses examined moderators including MI Spirit and patient baseline ratings of self-efficacy. RESULTS: There were no significant findings for the main effects models (Incidence Rate Ratio range .71-1.29). Only patient self-efficacy moderated the relationship between self-enhancement composite and 6 week outcome in the BNI condition; Self-enhancement composite was associated with lower frequency of drug use at 6 weeks in the BNI condition for those with low self-efficacy at baseline. Discussion: Overall, the results provided little support for the view that therapist skill in affirmation or enhancing self-efficacy was predictive of drug use outcomes in one-session interventions in primary care. The restricted range of interventionist skill ratings may account, in part, for these intervention process findings. Future work should explore the role of these interventionist variables on proximal indicators of change (i.e., intention) and drug use in MI-based interventions with demonstrated efficacy.