The effect of social learning on the nocebo effect: a systematic review and meta-analysis with recommendations for the future

Individuals frequently update their beliefs and behaviours by utilising information learned from observing the experience of others. While often adaptive, social learning has been implicated in the formation of negative health expectations, which subsequently lead to poorer health outcomes, a phenomenon known as the nocebo effect. The present systematic review and meta-analysis sought to evaluate: (1) whether social learning is sufficient to induce the nocebo effect; (2) any difference in the magnitude of socially-induced nocebo effects relative to other forms of induction (i.e., classical conditioning and/or explicit instruction); and (3) situational and dispositional factors that moderate these effects. Following a systematic literature search, twenty studies (n = 1,388) were included in the meta-analysis. The effect size for social learning ranged from medium-large relative to no treatment control conditions (Hedges’ g = .74) to small-medium when compared to neutral modelling control conditions (g = .42). The effect of social learning was similar in magnitude to classical conditioning but greater than explicit instruction with a small-medium effect size (g = .46). Face-to-face social modelling, longer modelling manipulations, studies with higher proportions of female participants and models, and greater observer empathy led to stronger socially-induced nocebo effects. However, further research is essential as only a minority of studies measured important constructs like negative expectancies and state anxiety. Results nevertheless demonstrate that social learning is a key pathway through which individuals experience nocebo effects and should therefore be a target for interventions to reduce the substantial personal and societal burden caused by nocebo effects.