2023 年 12 巻 1 号 p. 28-39
The planning fallacy refers to a cognitive bias wherein people underestimate the time it will take to complete tasks. Its degree is affected by unpacking. When a task is broken into components, each component is visualized, and the planning fallacy is reduced. This study examined the effects of unpacking at a more macro level by comparing single and multiple plans. The participants were 122 university students. They were first instructed to plan their exam study approximately ten days before the final Management Psychology exam. Some participants only planned about Management Psychology, while the rest planned about multiple subjects, including Management Psychology. During the exam, they answered a questionnaire about the actual time they spent studying and so on. Results showed no difference in exam scores between multiple-subject planners and single-subject planners. Planned study time and actual study time were shorter for multiple-subject planners. The plans as a whole were more detailed for multiple-subject planners, and the part of the plans concerning Management Psychology was simpler for multiple-subject planners. The multiple-subject planners may have studied more efficiently due to the unpacking effect. That implies that planning for multiple tasks simultaneously is more effective than planning for only one task.