Consider a part-time worker with an average of 16 shifts per month. At stores that attempted to make the changes, nearly 10 of those shifts were scheduled for a consistent time of day. At stores that had not done so, about nine of the shifts were consistent.

The explanation for how such modest changes could lead to such unusually large increases in sales may be that managers focused disproportionately on more experienced employees when it came to stabilizing the number of hours worked from week to week. That, in turn, appears to have lowered turnover among experienced workers, who helped their stores perform better.

“It looks like managers did the rational thing — they had to improve stability, and so they picked the more experienced people,” said Saravanan Kesavan, another author, who teaches business at the University of North Carolina. “Now you have more experienced people in the store, and the productivity you’re seeing increased, leading to higher sales.”

Mr. Kesavan suggested that Gap could reap still greater financial benefits by making schedules even more stable and reducing turnover beyond what the experiment achieved. “The attrition rate is still high,” he said. (Susan Lambert of the University of Chicago was the third author.)

The researchers chose the 28 stores in the study, then randomly selected the 19 where the new policies would take effect for just under a year. Although the managers in those stores had previously agreed to take part, the researchers could not be certain that they carried out all the new policies. The managers were simply urged to do so with the company’s blessing, an approach known as “randomized encouragement design.”

Marshall L. Fisher, a professor at the Wharton School at the University of Pennsylvania who is an expert on retailing and was not involved in the project, said the study provided compelling evidence that “if you treat people decently, you get better results.”