Neglect of Past Experiences in Prediction

Obstacles to Using Past Experiences

Despite the predictive value of past experiences, our findings suggest that people neglect them while forming predictions. Why might this be so? One answer was suggested previously: prediction, by its very nature, elicits a focus on the future rather than the past, and this future orientation may prevent individuals from looking backward. However, a failure to use personal base rates need not always result from inattention to the past. People may sometimes attend to their past, but nevertheless fail to incorporate this information into their predictions because it doesn’t seem relevant. People may have difficulty extracting an appropriate set of past experiences; the various instances seem so different from each other that individuals cannot compare them meaningfully (Kahneman & Lovallo, 1993; Kahneman & Tversky, 1979). As a British rugbyplayer-turned-commentator noted, “Each game is unique, and this one is no different [than] any other.”

We suggest that people often make attributions that diminish the relevance of past experiences to their current task (Ross & Fletcher, 1985). People are probably most inclined to deny the significance of their personal history when they dislike its apparent implications (e.g., that a project will take longer than they hope). If they are reminded of a past episode that could challenge their optimistic plans, they may invoke attributions that render the experience uninformative for the present forecast. This analysis is consistent with evidence that individuals are inclined to explain away negative personal outcomes (for reviews, see Miller & Ross, 1975; Snyder & Higgins, 1988; Taylor & Brown, 1988). People’s use of others’ experiences (population base rates) is also limited by perceptual and attributional factors: A focus on the future reduces the salience of others’ experiences, and the tendency to attribute others’ outcomes to their own dispositions (Jones & Nisbett, 1972) limits the inferential value of others’ experiences. Furthermore, our understanding of other people’s experiences is typically associated with uncertainty about what actually happened; consequently, we can readily cast doubt on the generalizability of those experiences. To quote Douglas Adams, “Human beings, who are almost unique in having the ability to learn from the experience of others, are also remarkable for their apparent disinclination to do so.”