Peak-End Rule

The peak-end rule is a psychological heuristic in which people judge a past experience mainly by how they felt at its most intense moment, the peak, and at its end, rather than through an average of the whole experience. The psychologists Barbara Fredrickson and Daniel Kahneman developed the underlying snapshot model of remembered utility in the 1990s, demonstrating the effect in a 1993 study using hand-immersion-in-cold-water experiments in which participants preferred a longer trial that ended with a slightly less painful final phase over a shorter trial that ended at its most painful point. A 1996 study by Kahneman and the physician Donald Redelmeier extended the finding to patients' memories of colonoscopy and lithotripsy procedures, showing that the remembered discomfort of a medical procedure tracked its peak and final intensity far more closely than its overall duration. The rule is closely related to duration neglect, the related finding that the length of an experience has little effect on how it is remembered, and it applies specifically to experiences with a clear beginning and end, holding for both pleasant and unpleasant experiences alike.