<p>This research aims to investigate the effects of different types of decision-makers (myopically rational, partially anticipated regret, and fully anticipated regret) in groups with various compositions, based on regret theory. The study begins with a theoretical framework that examines preference reversal due to partial (short-term) and full (long-term) regret-driven alterations in individual decision-making. To extend this analysis to group contexts, it designs a simulation-based study, predicting and comparing divergent probabilities of achieving specific outcomes across five group classifications and four composition scenarios within 2000 randomly generated simulations. The results demonstrate that regret significantly impacts group decision-making processes. Additionally, the study reveals that being part of a group in which one’s decision-making type is in the minority does not necessarily pose a disadvantage for myopically rational decision-makers, in contrast to regretful decision-makers. Moreover, strategically structured group compositions, through fixed types and weighted distributions, can lead to group outcomes that are better for individuals with specific types. This conceptual research highlights the critical role of regret-driven alterations in decision-making strategies, offering a theoretical framework for estimating the effect of regret on group decision-making.</p>