We examine how individuals become more overconfident in their knowledge when interacting with other decision makers. In three studies we test several possible explanations. The most consistent explanation for our findings is one of “rationale construction” where confidence increases by virtue of having to explain or justify one’s choices to others.

Heath, F. & Gonzalez, R. (1995). Interaction with others increases decision confidence: Evidence against information collection views of interactive decision making. Organizational Behavior and Human Decision Processes, 61, 305-326. doi:10.1006/obhd.1995.1024 (PDF) 

Abstract

We present three studies of interactive decision making, where decision makers interact with others before making a final decision alone. Because the theories of lay observers and social psychologists emphasize the role of information collection in interaction, we developed a series of tests of information collection. Two studies with sports collection show that interaction does not increase decision accuracy or meta-knowledge (calibration or resolution). The simplest test of information collection is responsiveness – that people should respond to information against their position by modifying their choices or at least lowering their confidence. Studies using traditional scenarios from the group polarization literature show little responsiveness, and even “deviants,” who interact with others who unanimously disagree with their choice, frequently fail to respond to the information they collect. The most consistent finding is that interaction increases people′s confidence in their decisions in both sports predictions and risky shift dilemmas. For predictions, confidence increases are not justified by increased accuracy. These results question theories of interaction which assume that people collect information during interaction (e.g., Persuasive Arguments Theory). They also question the labeling of previous results as “shifts” or “polarization.” We suggest that interaction is better understood as rationale construction than as information collection – interaction forces people to explain their choices to others, and a variety of previous research in social psychology has shown that explanation generation leads to increased confidence. In Study 3, we provide a preliminary test of rationale construction by showing that people increase in confidence when they construct a case for their position individually, without interaction.