Preference and Expectation for Treatment Assignment in a Randomized Controlled Trial of Once- vs Twice-weekly Yoga for Chronic Low Back Pain

BACKGROUND In studies involving nonpharmacological complementary and alternative medicine interventions, participant blinding is very difficult. Participant expectations may affect perceived benefit of therapy. In studies of yoga as treatment for chronic low back pain, little is known about the relationship between patient expectations and preferences on outcomes. This study was designed to identify baseline predictors of preference and to determine if expectations and preferences for different doses of yoga affect back-related function and low back pain intensity. METHODS This was a secondary data analysis of a 12-week randomized controlled trial comparing once-weekly vs twice-weekly yoga for treatment of chronic low back pain in 93 adults from a predominantly low-income minority population. At baseline, participants were asked about back function, back pain, treatment expectations, and treatment preferences. We created a variable "concordance" to describe the matching of participant preference to randomized treatment. Our outcome variables were change in back function and pain intensity after 12 weeks of yoga instruction. We performed logistic regression to identify predictors of preference for once- or twice-weekly yoga instruction. We created linear regression models to identify independent associations between expectations, preference, concordance, and outcomes. RESULTS Worse back function at baseline was associated with 20% higher odds of preferring twice-weekly yoga (OR 1.2, CI 1.1, 1.3). Individuals with higher expectation scores for twice-weekly yoga had 90% higher odds of preferring twice-weekly vs once-weekly yoga (OR 1.9, CI 1.3, 2.7). Individuals with higher expectation scores for once-weekly yoga had 40% less odds of preferring twice-weekly yoga (OR 0.6, CI 0.5, 0.9). After controlling for baseline characteristics, we found no statistically significant relationship between treatment outcomes, preference, expectation scores, or concordance. CONCLUSION In a population of predominantly low-income minority participants with chronic low back pain, worse back function was associated with preference for more frequent yoga classes. Those who preferred more yoga classes had higher expectations for those classes. Twelve-week change in back pain intensity and back function were not affected by dosing preference, expectation score, or concordance. More research is needed to better measure and quantify preference, expectations, and their relationship to outcomes in yoga research.