Social comparison interventions in promoting pro-environmental behavior: a meta-analytical and conceptual evaluation of randomized controlled trials

Social comparison interventions (SCIs) have been shown to promote pro-environmental behavior (PEB), yet observed effect sizes are typically small. Given their scalability and cost-effectiveness, SCIs hold substantial potential for population-level behavior change. A deeper examination of the social comparison process may enable the development of more targeted interventions that enhance positive outcomes. We synthesized existing evidence to assess the efficacy of SCIs in promoting PEB and their conceptual implementation in practice. We first conducted a systematic search in MEDLINE, PsycINFO, and Web of Science. Meta-analytic findings of 38 publications reporting 41 trials indicated that SCIs produced small effects compared to both passive and active control conditions, across both short-term and long-term evaluations (Hedges’ g s = 0.09 to 0.16; most ps < .05). However, substantial heterogeneity and prediction intervals that included the null indicate considerable variability across trials, suggesting that these effects may not consistently generalize and should be interpreted with caution. The conceptual review revealed that most trials addressed electricity or water use, relied on written formats, and used group averages as comparison sources. Comparison direction was generally unrestricted. Interventions were primarily framed around sustainability motives, with prevention-oriented messaging more common than promotion-oriented framing. Notably, none of the included trials reported participants’ appraisal of the motivational significance of the comparison outcome or whether the comparison end goal was perceived as attainable. These omissions limit understanding of the psychological mechanisms underlying SCI effects. We propose that SCI effectiveness can be strengthened by emphasizing the valuation process of comparison outcomes, incorporating personal and contextual determinants of behavior, and tailoring interventions to individual needs. Such refinements may increase the efficacy of SCIs in promoting effective and sustained PEB.