This paper provides the first empirical test of the diversification of opinions theory and the groupshift theory using real business data. Our data set covers management teams and single managersof US equity mutual funds. Our results reject the group shift theory and support thediversification...

We examine overconfidence among equity mutual fund managers. While overconfidencehas been extensively documented among retail investors, evidence fromprofessional investors is scarce. Consistent with theories of overconfidence, we findthat fund managers trade more after good past performance....