Limited research has examined individual differences in the accumulation of misinformation and unwarranted beliefs, known as contaminated mindware. The three unwarranted beliefs examined in this dissertation are paranormal, conspiracy, and anti-science beliefs. These beliefs remain prevalent in the public despite their epistemically suspect or unsubstantiated nature. This dissertation focused on the psychometric properties of items measuring individual differences in unwarranted beliefs to address three research objectives: (1) examine the underlying dimensional structure of unwarranted belief items in adolescents and young adults, (2) examine individual differences predicting susceptibility to these beliefs, and (3) examine differences between adolescents and young adults with respect to these beliefs. Study One examined the underlying structure of individual differences in unwarranted belief scores and its correlates in a sample of young-adults. Study Two confirmed that the same structure and correlates are found in adolescents. Both studies demonstrate the multidimensional nature of unwarranted beliefs that form domains of contaminated mindware. Specifically, the optimal factor model among adolescents and young adults was a hierarchical factor model with three correlated general factors (paranormal, conspiracy, and anti-science beliefs) and four specific paranormal factors (i.e., psi, superstition, spiritualism, and precognition). Further, we observed unique effects of individual differences in thinking and reasoning on individual differences in unwarranted beliefs. In Study Three, we assessed the measurement invariance of these scales across the two developmental groups, to allow for cross-sectional comparisons and age associations. The paranormal and conspiracy scales were characterized by strict invariance and the anti-science scale was characterized by strong invariance. With respect to developmental comparisons, endorsement of the unwarranted beliefs did not differ across development, except for a small difference in paranormal belief. Further, the unwarranted beliefs total scores were not associated with age. We discuss the novelty of the results within the belief literature on contaminated mindware and focus on the utility of this scale for future research
