Treatment expectations but not preference affect outcome in a trial of CBT and exercise for pain

Background: Patients' beliefs and attitudes toward a treatment can affect treatment response. In unblinded trials this can affect outcomes. Aims: The aim of this analysis was to examine the association between treatment preference and expectation and outcome in a trial of pain treatments. Methods: In a randomized trial (ISRCTN67013851) of four treatments for chronic widespread pain, participants were asked which they would prefer and what improvement they expect from each. The proportion of participants reporting positive health outcomes at three time points after treatment were compared between those matched or unmatched with their preference and between those with and without expectation for improvement. Odds ratios were calculated adjusted for baseline characteristics associated with preference and expectation. Results: Four hundred forty-two participants were recruited to the trial (69.5% female). The proportion reporting positive outcomes among participants matched to their preference compared to those unmatched was 33.3% vs. 34.4% at the end of treatment (adjusted odds ratio [aOR] = 0.80, 95% confidence interval [CI], 0.44-1.46), 34.4% vs. 29.0% at 3 months (aOR = 1.23, 95% CI, 0.67-2.26), and 34.8% vs. 30.3% at 2 years (aOR = 1.31, 95% CI, 0.70-2.46). The proportion of participants reporting positive outcomes among those expecting improvement compared to those not expecting improvement was 36.6% vs. 15.0% at the end of treatment (aOR = 2.03, 95% CI, 1.07-3.85), 34.1% vs. 13.2% at 3 months (aOR = 2.31, 95% CI, 1.22-4.38), and 32.8% vs. 19.1% at 2 years (aOR = 1.16, 95% CI, 0.67-2.36). Conclusions: Treatment preference had no clear effect on outcomes, but expectation did. These results could inform future approaches to management, and researchers assessing treatments should take into account this expectation effect.