Introduction: A growing body of evidence suggests that positive framing–inducing positive expectations about the outcome of treatments can reduce pain symptoms. However there is no pooled estimate of the effect size of positive framing for treating pain. Such an estimate is useful to understand the extent to which positive expectations can enhance usual care.

Methods: We extracted data from a recent systematic review of interventions that modified all "context factors" (including but not limited to) inducing positive expectations) in adults suffering from pain. The systematic review concluded that positive expectations were effective, but did not pool the results so no effect size was provided. Two authors independently extracted data from the studies and conducted the analysis. Our primary outcome was patient self-reported pain.

Results: 10 randomized trials were eligible for meta-analysis. In the trials with continuous outcomes the standardized effect size was −0.39 (95% confidence interval −0.68 to −0.10, p = 0.009, I² = 79%), suggesting reduced pain on average in groups in which positive expectations were induced. The effect size was similar in magnitude but was not statistically significant when we excluded studies deemed to have a high risk of bias (standard effect size −0.31, 95% CI −0.65 to 0.02, p = 0.07, I² = 77%).

Conclusion: The effect of inducing positive expectations is comparable to the effects of some pharmacological drugs. However many of the studies had a high risk of bias, and heterogeneity was significant. Future research is warranted including investigating ways to implement this evidence into patient care in an ethical way.