Validation of the confidence proxy (Conf). Our proxy for confidence (Conf = square of centered likeability rating or choice likelihood) was tested against confidence ratings collected in independent datasets. Left, In the likeability rating task (Lopez-Persem et al., 2020), participants first rated the likeability of food, face, and painting items and then provided a confidence rating about their own likeability judgment. Right, In the A/B binary choice task (Lee and Daunizeau, 2020), participants selected their preferred item between options shown in pairs, and then provided a confidence rating about having made the best choice. Graphs represent confidence rating as a function of binned Conf. Dots represent means over participants. Error bars indicate interparticipant SEs. Dotted lines indicate linear regression fits.