Supplementary material from "On the Nature of Certainty in Value-Based Evaluations: Disentangling Variability- and Extremity of Experiences"

Consistent value-based decision-making is crucial for outcomes such as maintaining a healthy lifestyle, or being perceived as trustworthy. Certainty in evaluations is related to consistency of value-based decisions, but its nature is poorly understood. Here we examined how evaluation certainty is formed through the possibly unique contributions of “variability”- and “value-extremity” of prior experiences with objects. We conducted a preregistered 2×2 within-subjects experiment (N = 188) where variability- and value-extremity of experiences with objects were manipulated independently. Participants learned value-distributions for objects, estimated their value, and rated certainty in their evaluation. As predicted, results show that variability of experiences is negatively related to evaluation certainty, independent of value-extremity. Surprisingly, we find no evidence for a positive effect of value-extremity on evaluation certainty. These results point to the possibility that the previously observed relation between value-extremity and evaluation certainty is the result of an ecological confound between variability and value-extremity of prior experiences.