Examination of self-determination theory constructs as mediators of the effect of motivational interviewing on tobacco cessation outcomes

Abstract

Despite an abundance of evidence supporting the efficacy of motivational interviewing for health behavior change, little is known about how it works. This study conducted a secondary analysis of autonomous motivation as a mediator of motivational interviewing’s effects in a recently completed randomized controlled clinical trial comparing motivational interviewing to health education on smoking quit attempts (KC Quest). Results of the parent trial unexpectedly revealed that motivational interviewing was not more effective than health education for inducing quit attempts of smoking cessation. While the mechanism through with the interventions is still unknown it remains feasible that motivational interviewing led to quit attempts and cessation by increasing autonomous motivation while health education was effective through a different mechanism. Interventions consisted of motivational interviewing (n=90) and health education (n=92). The primary outcome was the occurrence of any quit attempt defined as a serious quit attempt of at least 24 hours (Biener & Abrams, 1991; Marlatt, Curry, & Gordon, 1988) by Week 26. The Treatment Self-Regulation Questionnaire (TSRQ), developed from self-determination theory (SDT:Deci & Ryan, 1985), assesses the degree of autonomous self-regulation regarding why people engage or would engage in healthy behavior. Change scores from baseline to week 26 in the Autonomous (AR) and Controlled regulation (CR) subscales were computed for use in the mediation modeling. Log-binomial regression mediation examining each mediator separately revealed neither AR nor CR mediated effects of motivational interviewing or health education on quit attempts. A strength of the KC Quest enrollment was the inclusion of a racially diverse group of participants (67.2% Black) most adversely effected by smoking co-morbidities. Our current study did not detect a difference in smoking outcomes based on motivation mediators among Black participants. An important implication of this study is that while self-regulation failed to explain how, motivational interviewing and health education both increased quit attempts. There is a need for future investigations to examine other SDT constructs, such as relatedness and competence, as potential mediators of smoking interventions.