An empirical study on planning fallacy

Effect of task difficulty

Abstract

The tendency to underestimate the time required to complete a project, even while knowing that the vast majority of similar projects have run late, has been termed the “planning fallacy” (Kahneman & Tversky, 1979). Although many studies have shown that people often underestimate their task-completion time, the mechanism of the planning fallacy has not become clear. In order to verify the mechanism, this article conducted two experimental studies from the perspective of task difficulty. In Study 1, participants predicted the necessary times of two tasks (easy task and difficult task) and worked on them. As a result of Study 1, it was demonstrated that the task difficulty affected the degree of the planning fallacy. Participants underestimated the necessary time of easy task, but on the other hand participants overestimated the necessary time of difficult one; the difference was statistically significant (p < .01). Study 2 was conducted one year after the Study 1. In Study 2, participants recalled the task-completion times of two tasks which they had worked on one year ago. As a result of Study 2, it is shown that the task difficulty also affected the degree of the memory bias. Participants underestimated the task-completion time of easy task which they had worked on one year ago, whereas overestimated the task-completion time of difficult one; the difference was statistically significant (p < .01).