Does practice quality mediate the relationship between practice time and outcome in mindfulness-based stress reduction?

Interventions based on mindfulness meditation are increasingly common and evidence exists supporting their use. However, questions remain regarding treatment mechanisms accounting for beneficial effects. The current study examined one candidate mechanism – mindfulness practice quality – as a mediator of the link between practice time and outcome within mindfulness-based stress reduction (MBSR). Participants (n=96) completed measures of mindfulness and psychological symptoms at baseline and post-treatment. A weekly questionnaire assessed practice time and quality over the eight weeks of MBSR. Multilevel models accounted for nesting within participants, MBSR groups, and instructors. Results generally supported the reliability and validity of a weekly single-item practice quality measure. Greater practice time was associated with improved practice quality (r=.48). Increases in practice quality predicted improvements in self-report mindfulness and psychological symptoms (bs=.35, .30, and -.19, ps<.05,), but not behavioral mindfulness (b=-.02, p=.879). In multilevel mediation models, improved practice quality mediated the link between practice time and changes in self-report mindfulness, suggesting improved practice quality functions as a mechanism linking practice time and outcome in MBSR. Future research evaluating practice quality in clinical samples, in tandem with intensive sampling paradigms (e.g., experience sampling) and objective (behavioral, physiological) outcomes may be warranted.