Insufficient evidence to determine the impact of patient preferences on clinical outcomes in acupuncture trials: a systematic review.

OBJECTIVE: To review reporting of preferences in acupuncture studies and their effect on clinical outcomes. STUDY DESIGN AND
SETTING: Systematic review of published randomized and quasi-randomized controlled trials of acupuncture reporting participant preferences for randomization or treatment or using a preference design.
RESULTS: Of the 31 included trials, 5 reported on randomization preference, 18 on treatment preference, and 1 reported on both. Seven used a preference design. Four out of seven trials noted that the group with preferences had different baseline characteristics (less education, worse baseline measure score, and greater or fewer years with pain). There was a tendency for greater attrition in nonpreference arms at 6 months but not earlier. Around three-quarters of participants turned down randomization in favor of nontrial treatment, and preference for acupuncture was around 20% when offered multiple treatments. Questions used to elicit preferences varied across trials and were poorly reported. Ten trials reported the effects of preferences on outcomes; only one detected a statistically (but not clinically) significant difference.
CONCLUSION: There is little evidence that preferences cause detectable effects on outcomes in acupuncture trials; however, trials use inconsistent methods and poorly report these data. Monitoring the level and effect of preferences in trials is recommended.