Hindsight ≠ foresight: the effect of outcome knowledge on judgment under uncertainty*
- Correspondence to: B Fischhoff, Hebrew University of Jerusalem, Israel
One major difference between historical and nonhistorical judgment is that the historical judge typically knows how things turned out. In Experiment 1, receipt of such outcome knowledge was found to increase the postdicted likelihood of reported events and change the perceived relevance of event descriptive data, regardless of the likelihood of the outcome and the truth of the report. Judges were, however, largely unaware of the effect that outcome knowledge had on their perceptions. As a result, they overestimated what they would have known without outcome knowledge (Experiment 2), as well as what others (Experiment 3) actually did know without outcome knowledge. It is argued that this lack of awareness can seriously restrict one’s ability to judge or learn from the past.
↵* Copies of these stimuli with the four offered outcomes will be supplied with all requested reprints. The permission granted by the Oxford University Press and Ronald Press to use these copyrighted materials is gratefully acknowledged.
↵† It might be wondered whether Before subjects might not behave like After subjects with reference to their predictions, which they know are actually postdictions. In a series of five experiments (Fischhoff, in press), we found that manipulating the temporal setting of possible outcomes has no effect on their perceived likelihood.
↵* This is a reprint of a paper that appeared in Journal of Experimental Psychology: Human Perception and Performance 1975, Volume 1, pages 288–299. Copyright © 1975, Psychological Association. Reprinted with permission.
Preparation of this report was supported by the Advanced Research Projects Agency of the Department of Defense (ARPA Order 2449) and was monitored by the Office of Naval Research under Contract No. N00014-73-C-0438 (NR 197026). The research reported constitutes part of a doctoral dissertation submitted to The Hebrew University of Jerusalem. I am deeply indebted to Amos Tversky, Daniel Kahneman, Paul Slovic, Ruth Beyth, and Sarah Lichtenstein for their contributions to this project. The detailed comments of two anonymous reviewers on a previous draft are gratefully acknowledged.