The Dunning-Kruger effect does not account for Covid-scepticism or vaccine hesitancy

Vaccine-scepticism and vaccine hesitancy are sometimes explained using the Dunning-Kruger effect (DKE), which posits that individuals with low knowledge in relevant domains are overconfident in their understanding. However, prior evidence often relies on discrepancy-based measures of self-overestimation that are susceptible to statistical artefacts. It, therefore, remains unclear whether vaccine-scepticism genuinely reflects the defining features of the DKE. During the Covid-19 pandemic, a large UK sample (n = 537) completed a newly developed Covid-scepticism (CS) scale, with a knowledge test assessing biological knowledge and probabilistic reasoning, relevant to a viral pandemic. Item-level confidence ratings for each knowledge judgement were used to derive a measure of metacognitive bias, which indexes a person's overall tendency towards low or high confidence. Higher CS was associated with lower levels of knowledge. The relationship with low knowledge was strongest for sceptical attitudes towards vaccines and endorsement of conspiracy-adjacent beliefs. However, lower knowledge was not associated with overconfidence, as predicted by DKE accounts. Instead, metacognitive bias increased with knowledge, and higher vaccine-scepticism predicted lower overall confidence. These findings provide little support for accounts of vaccine-scepticism based primarily on the popular view of the DKE. The results underscore the importance of using appropriate measures of metacognition and caution against dismissive characterizations of vaccine-sceptic attitudes.