ABSTRACT

The hindsight bias or knew-it-all-along effect (Fischhoff, 1975, 1977) is the tendency to retrospectively exaggerate one’s foresight knowledge about the outcome of an event. This phenomenon has been found in experimental settings (e.g., Dehn & Erdfelder, 1998; Hell, Gigerenzer, Gauggel, Mall & Müller, 1988, see overview by Hawkins & Hastie, 1990) and in a variety of applied settings as well, for example, in medical diagnoses (Arkes, Faust, Guilmette, & Hart, 1988; Detmer, Fryback, & Gassner, 1978), jurors’ decisions (Casper, Benedict, & Perry, 1989) or judgements of historical-political events (Fischhoff, 1975; Pennington, 1981a; Wasserman, Lempert, & Hastie, 1991). Several studies have also investigated the phenomenon of concern in the present article, namely, hindsight bias in political elections (Fischer & Budescu, 1995; Leary, 1982; Penningon, 1981b; Powell, 1988; Synodinos, 1986; Tykocinski, 2001; Wendt, 1993), and in most of these studies some evidence for hindsight bias was found. Upon closer examination, however, these effects appear to be quite heterogeneous and do not readily fit into a coherent picture. Hindsight bias was found most easily for confidence judgements and, to a lesser extent, for

probability estimates, but not consistently for the predicted percentage of votes. To illustrate, Synodinos (1986) asked 217 students, on the day prior to the election, about the outcome of the Hawaiian gubernatorial election in 1982. His participants predicted the percentage of votes that each of three candidates would receive, indicated their confidence for these predictions, and further estimated the probability that each candidate would win the election. Another 257 participants made the same judgements in retrospect 2 days after the election. In other words, Synodinos used a between-participants hypothetical design in which some participants make foresight judgements concerning some event and others make the same judgements in hindsight as if they had not known the outcome. As it turned out, there was no significant difference between the pre-election and post-election samples for the estimated percentage of votes. However, the post-election participants were significantly

Requests for reprints should be sent to Dr Hartmut Blank, Institut für Allgemeine Psychologie, Universität Leipzig, Seeburgstr. 14-20, D-04103 Leipzig, Germany. Email: blank@rz.uni-leipzig.deThe preparation of this article was supported by Grant Er224/l-2 from the Deutsche Forschungsgemeinschaft (DFG). We are strongly indebted to Martin Beckenkamp of the University of Saarbrucken for his generous support in the conduction of our second study. We also thank the participants of the first and second Hindsight Bias workshops in Mannheim and Rauischholzhausen, sponsored by the DFG (SFB 504) and the University of Giessen, respectively, for fruitful discussions of our studies. Study 2 was mainly inspired by the Mannheim workshop. Finally, we are grateful to Mark Elliott, Oliver Hardt, and Stefan Schwarz for helpful comments on a previous version of this article.