Pain-Reporting Variability and Reliability as Predictors of Placebo Effects: A Cross-Sectional Experimental Pain Study

The study examined whether variability and reliability of pain reporting predict placebo analgesia in 803 participants (401 with temporomandibular disorder and 400 healthy controls). Participants completed a standardized thermal pain protocol with calibration, conditioning, and testing phases. Pain-reporting variability was measured using standard deviation and coefficient of variation, while reliability was assessed using intraclass correlation coefficients. Greater pain-reporting variability during the conditioning phase was associated with reduced placebo analgesia, mediated by slower acquisition of the cue-pain contingency. Thermal pain response variability during calibration did not predict placebo effects. Individual differences in pain-reporting variability during the learning phase proved more important than general sensory variability in determining the magnitude of placebo effects.