Abstract
This paper complements the 20-item prosopagnosia index (PI20), which is a self-report measure of developmental prosopagnosia (DP) developed by Shah et al. (2015, R. Soc. Open. Sci. 2, 150305. [doi: 10.1098/rsos.140343]). Although they validated PI20 in several ways and it can serve as a quick and cost-effective measure for estimating DP risk, they did not formally evaluate its validity against a pre-existing alternative questionnaire (Kennerknecht et al., Am. J. Med. Genet. A 146A, 2863-2870. [doi: 10.1002/ajmg.a.32552]). Thus, we administered the questionnaires to a large population (N=855) and found a very strong correlation (r=0.82 [95% confidence interval: 0.80, 0.84]), a principal component that accounted for more than 90%of the variance, and comparable reliability between the questionnaires. These results suggest unidimensionality and equivalence between the two questionnaires, or at least, a very strong common latent factor underlying them.