Some disagreement makes groups more trustworthy, mathematical framework finds

September 5, 2026 feature Some disagreement makes groups more trustworthy, mathematical framework finds Ingrid Fadelli Author Sadie Harley Scientific Editor Robert Egan Senior Editor When humans are making decisions, they are known not to rely solely on their own considerations and the evidence available to them. Past behavioral science and psychology studies have shown that people are often also influenced by the choices and opinions of others. For example, many people tend to conform to the judgments and opinions of the majority, even if they conflict with their own or with the information they are presented with. In behavioral science, this tendency is referred to as conformity bias. Researchers at the University of Toulouse-CNRS and the University of Leeds recently used a mathematical approach to investigate how groups of experts make decisions and whether dissent influences the reliability of their choices. Their findings, published in the Journal of the Royal Society Interface, suggest that high levels of agreement or unanimity during group decision-making are not always signs of expertise and trustworthiness. "While reading a previous paper, we realized that a paradoxical—yet intuitive—result could emerge from Bayesian decision-making," Aurèle Boussard, first author of the paper, told Phys.org. "In this mathematical framework, individuals balance private and social information in an optimal way. From that, it reasonably follows that the more individuals agree, the more likely the group is to be right. However, we found situations leading to the opposite conclusion, in which the more confident a group seems, the less trustworthy it is." Exploring the implications of high conformity Earlier observations by behavioral scientists suggest that a group's overconfidence in a decision can sometimes indicate conformity bias or other cognitive biases. In other words, individuals in the group might have simply agreed with the decision that the majority was leaning toward or may have made an unconsidered choice. "We were surprised to predict a lower majority accuracy at high agreement (compared with slightly lower agreement, i.e., some dissent), so we decided to investigate," explained Boussard. "We started with the basic tools of probability theory to model how an individual would make the best decision given some information (both private and social). This is an idealized version of reality in which individuals are not assumed to be cognitively biased. That idealization is, however, useful because it gives a clear baseline to which we can add specific biases, such as conformity—the tendency to align one's judgment with a group." There are numerous different ways of mathematically modeling conformity. In their paper, Boussard and colleagues used four distinct formulations: two information transfer schemes and two mathematical models. "We also varied the complexity of the decision, which is represented by the quality of the private information available to each individual," said Boussard. "This produced 16 model cases, intended to cover many plausible real-life group decisions." For every case they delineated, the researchers calculated the probability that most decision-makers were correct as a function of the agreement between them. This allowed them to test whether group confidence is a good indicator of trustworthiness and decision quality. "From this relationship, we computed the probability that accuracy declined as agreement increased," explained Boussard. "We term this phenomenon 'credibility-enhancing dissent.' This is a pattern in which groups that appear more confident are in fact less trustworthy. Except when decisions are overly simple, optimal decision-making with conformity makes credibility-enhancing dissent possible." Why some dissent is a hint of reliability The team's findings suggest that when conformity bias is absent, the accuracy and trustworthiness of group decisions steadily increase along with agreement between members. However, when this bias is considered, unanimity or high levels of agreement are no longer reliable indicators of trustworthiness and decision quality. "The contribution I value most is bringing the level of agreement into the evaluation of collective reliability," said Boussard. "In real-life decisions, agreement is a highly accessible signal, yet a purely rational view would wrongly treat it as an indicator of trustworthiness. "Reality is always more complex than purely rational behavior, and conformity is widely shared among social species, in part because it promotes cohesion. Since conformity is common in social species, the presence of dissent is likely to be a good sign." Boussard and colleagues showed that in a realistic scenario in which people may exhibit conformity bias, high levels of agreement tend to be a sign of trustworthiness only when the decision to be made is fairly simple. When a choice is harder, on the other hand, some dissent could be a sign that members of the group were less influenced by each other when trying to reach a shared conclusion. Many past studies investigated collective decision-making by examining the behavior or actions of individual members in a group. Boussard and colleagues took a different approach, focusing on collective decisions from the outside, without any knowledge of internal group dynamics. "While this seems a less obvious case, it happens all the time in real life: We are often faced with the task of judging the validity of a decision made by a group of experts or leaders—but also friends or colleagues," said Boussard. "In this field, as in any modeling field, we try to cope with the constraints of reality by focusing on what matters most. To make this possible, our models only consider binary choices in which individuals decide sequentially based on information represented by a single variable. With conformity (likewise represented by a single variable), our models predict credibility-enhancing dissent to appear quite often." Guiding future research into decision-making Rather than showing that consensus is always a sign of unreliable decisions, this study suggests that consensus alone is not a strong enough marker of a decision's quality. The team's findings could soon inspire other behavioral scientists to examine biases and decision-making using mathematical approaches. In the future, the researchers' efforts could help improve existing models of collective decision-making, potentially helping to devise new strategies to improve the reliability of group decisions in various fields. As part of his next studies, Boussard plans to also explore how other cognitive biases may interact with conformity and agreement within groups. "I would also enjoy working with experimentalists, because testing this kind of model against behavioral data is a valuable and exciting challenge," added Boussard. "A second theme I find particularly stimulating is cultural evolution, or, in other words, how the ways a social species makes collective decisions can shape and be shaped by the traits that persist through the historical development of a culture. One fascinating question is how departures from rationality in collective decision-making may either support or undermine the long-term persistence of cultural practices and, more broadly, cultural sustainability." Written for you by our author Ingrid Fadelli, edited by Sadie Harley, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a donation (especially monthly). You'll get an ad-free account as a thank-you. Publication details Aurèle Boussard et al, Dissent enhances the credibility of groups of Bayesian conformist decision-makers, Journal of the Royal Society Interface (2026). DOI: 10.1098/rsif.2025.0956. Journal information: Journal of the Royal Society Interface © 2026 Science X Network