Philip Meißner, Torsten Wulf

• Teams of business leaders make most strategic decisions in organizations. However, although a large body of research has analyzed cognitive biases of individual leaders, little is known about how those biases affect teams on the group level. Therefore, on the basis of research into group decision making and group diversity, we analyze demographic diversity and group tenure as two important determinants of overconfidence in groups. We report findings from a quasi-experimental field study iolving 46 management teams, which suggest that diversity and tenure have separate, direct effects on group overconfidence. More specifically, we show that demographic diversity reduces group overconfidence, while group tenure increases it. These findings add a dynamic dimension to the conceptualization of group overconfidence in teams. Keywords: Group overconfidence, demographic diversity, tenure