Overall, 72 subjects invest their endowment in four risky assets. Each com-bination of assets yields the same expected return and variance of returns. Illusion of expertise prevails when one prefers nevertheless the self-selected portfolio. After being randomly assigned to groups of four...

Two participants have to decide jointly, with the discussions preceding their choice being video/audiotaped. For two tasks, one with and one without strategic interaction, we refer to obvious reasoning styles as mental models. The videotaped discussions are analyzed according to which mental...