WE are in the Islamic holy month of Ramadan. During this time, as prescribed by one of the five “pillars,” or obligations, that make up the foundation of Muslim life, hundreds of millions of followers are abstaining from eating and drinking (and a host of other activities, like smoking and sex) between dawn and sunset.

This fasting does not burden all the world’s Muslims equally. For Muslims who live in the Northern Hemisphere, the day is longer at this time of year than it is in the Southern Hemisphere — which leads to longer fasts.

But this isn’t always the case. The Islamic calendar is lunar (around 354 days) and does not incorporate leap years, so Ramadan rotates slowly through the Western calendar, year after year, 11 days at a time. In a decade and a half, Ramadan will fall during the shorter days of winter in the Northern Hemisphere, while Muslims in southern locales like Australia and South Africa will face longer fasts.

This cyclical feature of Ramadan turns out to be a handy tool for social scientists. As we demonstrate in a working paper for the National Bureau of Economic Research, it helps us address a longstanding question: Does religion — specifically, the practice of religious rituals — affect economic growth?