Unfounded beliefs online: a socially adapted theory of planned behaviour model for misinformation adoption and spread

The spread of misinformation on social media is shaped not just by what people believe to be true, but by identity and group-based motivations. In this study, we adapt the Theory of Planned Behaviour (TPB) to examine how social identity, perceived in-group agreement, and perceived sharing efficacy influence belief in and willingness to share misinformation targeting out-groups. A U.S. sample (N = 455) evaluated true and false stimuli, and path analysis was used to test the TPB model across multiple social groups. We use multi-group analysis to assess the roles of social factors in believing and sharing group-congruent misinformation. Perceived credibility was the strongest predictor of sharing across all groups; however, in most models, social identity and perceived in-group norms also directly predicted willingness to share, even after accounting for perceived credibility. This suggests that sharing misinformation often serves a signalling function, independent of perceived accuracy. This effect holds across a variety of social identity groups, including politics, ethnicity, religion, and sexual orientation. Sharing efficacy also predicted sharing in most cases, particularly for content that aligned with the individual’s identity. An updated model that included direct effects from identity and norms to sharing significantly improved model fit in all groups. Significant, direct pathways suggest that misinformation sharing is shaped by identity, social expectation, and perceived expressive value, rather than accuracy alone. The adapted TPB model further explores social motivations for sharing behaviours and adds to the psychological understanding of how and why misinformation spreads online.