Uncorrected Proof Overconfidence in Predictions as an Effect of Desirability Bias F. Giardini, G. Coricelli, M. Joffily, and A. Sirigu Keywords: Decision making · Overconfidence · Reward · Desirability · Accuracy AQ: Please specify corresponding author. 1 Introduction Most people hold unrealistic positive beliefs about their personal skills, their knowledge (Fischoff, Slovic, & Lichtenstein, 1977), and their possibilities to overcome the performance of other individuals (Weinstein, 1980). This general tendency, called overconfidence, is a stable and pervasive finding both in many real-life domains and in several experimental settings. People are overconfident about their driving skills (Svenson, 1981), about their ability as basketball play- ers (McGraw, Mellers, & Ritov, 2004), about their competence in financial and managerial problems (Camerer & Lovallo, 1999; Mahajan, 1992), and about their general knowledge (Juslin, 1994; Harvey, 1997). This systematic overestimation of one’s own capabilities and probabilities of success can have important conse- quences, and sometimes results in suboptimal decisions. While the existence of overconfidence is uncontroversial, its sources and de- terminants are still open to debate (Ayton & McClelland, 1997; Klayaman, Soll, Gonzalez-Vallejo, & Barlas, 1999). In this study we contribute to this debate by demonstrating that overconfidence in predictions is related to the desirability of the predicted outcome. When people F. Giardini Institute of Cognitive Sciences and Technologies (ISTC), National Research Council, Via San Martino della Battaglia, 44, 00185, Rome, Italy e-mail: francesca.giardini@istc.cnr.it G. Coricelli, M. Joffily and A. Sirigu Institut des Sciences Cognitives, CNRS, 67, Boulevard Pinel, 69675, Bron, France e-mail: coricelli@isc.cnr.fr; joffily@isc.cnr.fr; sirigu@isc.cnr.fr M. Abdellaoui, J.D. Hey (eds.), Advances in Decision Making Under Risk and Uncertainty. 163 Theory and Decision Library C 42. c  Springer-Verlag Berlin Heidelberg 2008