The 2015 analysis of this data showed that as hours worked increased, output also increased, but only to a point. Output per hour peaked at about 40 hours of work per week and then fell.
Study author Dr John H Pencavel, a professor in the economics department at Stanford University, suggests there’s a sweet spot in the number of hours people work per week. “After a point (a point that probably varies across workers and across their tasks), one more hour of work delivers more output (or better performance) if the worker has already worked 30 hours a week than if the worker has already worked 40 hours a week,” he says via email.
Pencavel discusses the same munitions workers in his book Diminishing Returns at Work: The Consequences of Long Working Hours. There he explains that the workers typically put in more than 50 hours of work per week, and sometimes as many as 72. Pencavel’s number-crunching shows that the weeks when output was highest were not the same weeks when the hours were longest.
This means that, at a certain point, throwing more hours at the problem doesn’t help – and only runs up the operational costs.
Taking time off
It’s not just about working hours: days off are also important when it comes to productivity. Munitions workers often worked many days in a row without rest. Saturday work was still common then, and Sundays were reinstituted as workdays because of the war.
Occasionally, however, munitionettes got to take a Sunday off. The HMWC collected data covering both these conditions and realised that a work week without a day of rest doesn’t benefit anyone. Output does not increase, and workers are unhappy.