In belief change, message discrepancy is the difference between the belief position advocated in a message and a message receiver’s initial belief position. Psychological discrepancy is the message discrepancy experienced by the receiver. Existing literature had assumed that a high level of psychological discrepancy discounted the weight of a message, which could make the message less effective. However, there were three alternative assumptions about the role of psychological discrepancy. The problem that this dissertation examined was: Does psychological discrepancy affect the weight of a message only, affect the scale value of the message only, affect neither, or affect both? To find out which of these four assumptions was more plausible, this dissertation derived competing hypotheses based on four mathematical models either through an analytic proof alone or a combination of an analytic proof and a computational approximation. This dissertation tested these hypotheses in an experiment with a 3 (high vs. moderate vs. low message scale value) ´ 3 (high vs. moderate vs. low upper bound) between-subjects design (N = 448 Mechanical Turk workers). The results showed that the weight-discounting model had the most supported hypotheses and fit the data the best, which indicated that psychological discrepancy affected the weight of a message only. This dissertation improves the understanding of the mechanism that leads to the outcomes posited by discrepancy models in persuasion research and provides additional empirical evidence for the scale value constancy assumption in information integration theory. / Media & Communication