The link between time-of-day and productivity on cognitive tasks is crucial to understand workplace efficiency and welfare. A new IZA paper by Alessio Gaggero and Denni Tommasi examines the performance of university students taking at most one exam per day in the final two weeks of the semester. Exams are scheduled at different time-of-day in a quasi-random fashion.
Analyzing data on half a million student-exam level observations, the authors find that peak performance occurs around lunchtime (1.30pm), as compared to morning (9am) or late afternoon (4.30pm). This inverse U-shaped relationship between time-of-day and performance (i) is not driven by stress or fatigue, (ii) is consistent with the idea that cognitive functioning is an important determinant of productivity and (iii) implies that efficiency gains of up to 0.14 standard deviations can be achieved through simple re-arrangements of the time of exams.
While previous research has shown that biological factors influence changes in productivity between day and night shifts, this study establishes that such a relationship is also important within a standard daylight shift.
The study also found that the time-of-day effects varied seasonally, depending on the sunlight-related circadian rhythm: Moving an exam from the morning to lunchtime in January increases a student’s performance twice as much as in June.
A simple back-of-the-envelope calculation applied to an external context that is likely to benefit from these results—elective surgeries—suggests that a different sorting of the cognitive tasks performed by surgeons may lead to an increase in the number of patients saved during surgery.
Read also an article about this paper in MONEY.