https://phys.org/news/2018-07-four-day-weeks-days.html

The analysis shows that employees working four-day weeks felt better about their job, were more engaged, and generally reported greater work-life balance and less stress—all while maintaining the same level of productivity. Interestingly, they also experienced a small but significant decrease in work demands.

The company asked its 240 office workers to work a four-day week (at eight hours per day) instead of five days, while still being paid their usual five-day salary. The trial was inspired by growing evidence that modern open-plan workplaces can be distracting for workers and reduce productivity.