"Cognitive Fatigue" and Task Performance

Increasing the number of days between exams from one to ten improves the probability of passing both exams by 8 percent.

In many education and work environments, students or workers must perform several mental tasks in a short period of time. And just as with physical fatigue, cognitive fatigue can occur, and can affect performance if those tasks are scheduled close together.

In The Impact of Time Between Cognitive Tasks on Performance: Evidence from Advanced Placement Exams (NBER Working Paper No. 18436), Ian Fillmore and Devin Pope analyze data on a 10-percent sample of all Advanced Placement (AP) exam takers who took two (and only two) exams in the same year between 1996 and 2001. Their sample consists of thousands of students who were tested on the same two AP subjects but with varied time gaps between their two exams.

They find that performance improves significantly with more days between exams. Increasing the number of days between exams from one to ten improves the probability of passing both exams by 8 percent.

The authors also find that the relationship between total points on the two exams and time between the exams is almost entirely linear, which suggests that increasing the time between exams from one to three days has a similar impact on performance as increasing the time between exams from eight to ten days. Furthermore, the benefit of more spacing between exams is driven almost entirely by the increase in performance on the second exam. They discover some differences across demographic groups, with women and Asians benefitting more than other groups from increasing the time between exams.

--Lester Picker