Mechanisms of Action in Motivational Interviewing
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Abstract
Despite the demonstrated efficacy of disease modifying therapies (DMT), many MS patients (~ 40%) stop using DMT within 3 years of starting. A cross-over randomized controlled trial demonstrated that a theoretically based motivational interviewing- cognitive behavior therapy (MI-CBT) intervention increased DMT re-initiation among relapsing-remitting MS patients compared to a treatment as usual (TAU) condition. This study explored the mechanisms of action responsible for the effectiveness of the MI-CBT intervention. Following baseline assessment, participants (N=91; 85.7% female) were randomly assigned to receive either five sessions of MI-CBT or to treatment as usual with brief education. Potential mediators were two broad measures of motivation (a single item motivation “ruler” and the Brief Motivation Scale; BMS), autonomous motivation, personal control, treatment control, and confidence to re-initiate). They were assessed at baseline and end of treatment (week 10) using established measures. Log-binomial regression mediation examining each mediator separately revealed that the strongest mediators were the motivation ruler and BMS. The intervention was associated with an estimated 20% increase in probability of positive outcome through its effect on the motivation ruler and an estimated 24% increase of positive outcome through its effect on BMS. In exploratory regression analyses that examined each of the mediators as predictors of DMT (re-) initiation in a comprehensive logistic regression model, the only significant predictor in the model was the BMS change variable. A second logistic regression model in which the Brief Motivation Scale change predictor variable was removed, revealed that the motivation ruler and the personal control change variable were significant predictors of (re-) initiation. An important implication of this study is that the MI-CBT intervention appeared to work primarily by increasing motivation rather than by increasing confidence. This study also highlights the importance of personal control in promoting DMT re-initiation and the need for future studies to investigate other interventions to promote personal control in patients with MS.
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Introduction -- Background -- Methodology -- Analyses -- Results -- Discussion -- References -- Appendix A. Brief Motivation Scale -- Appendix B. Motivation and Confidence Rulers -- Appendix .C. Treatment Questionnaire concerning Multiple Sclerosis -- Appendix D. Revised Illness Perception Questionaire
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Ph.D. (Doctor of Philosophy)