Confirmatory bias in health decisions: Evidence from the MMR-autism controversy.

Since Wakefield et al. (1998), the public was exposed to mixed information surrounding the claim that measles-mumps-rubella vaccine causes autism. A persistent trend to delay the vaccination during 1998-2011 in the US was driven by children of college-educated mothers, suggesting that these mothers held biases against the vaccine influenced by the early unfounded claim. Consistent with confirmatory bias, exposures to negative information about the vaccine strengthened their biases more than exposures to positive information attenuated them. Positive online information, however, had strong impacts on vaccination decisions, suggesting that online dissemination of vaccine-safety information may help tackle the sticky misinformation.