The Impact of prior task experience on bias in predictions of duration

The effect of prior experience on bias in time predictions on two different types of laboratory task was examined in two studies. Experiment 1 revealed that prior experience of performing a substantial part of the same task led to greater time prediction accuracy. However, contrary to the weight of previous research, there was little evidence of the temporal underestimation indicative of the planning fallacy. In fact, temporal underestimation only occurred on a longer duration task when it was preceded by a much shorter task, which was either related (Experiments 1 and 2) or unrelated to it (Experiment 2). In contrast, temporal overestimation prevailed on tasks ranging from about 30 seconds’ to four minutes’ duration. Contrary to the theory of the planning fallacy, these studies indicate that people do take account of their performance on previous tasks and use such distributional information when predicting task duration. The potential role of the anchoring and adjustment cognitive heuristics in determining temporal misestimation is discussed.