What constitutes a “normal” night’s sleep?

That all depends, says Danny Forger, a biological mathematician at the University of Michigan and an expert in circadian clocks.

“People set guidelines all the time – you need eight hours, you need seven hours – but we’ve found that ‘normal’ sleep varies tremendously depending on your age, sex and what country you are in,” he said.

Forger is the senior author of a new study that analyzed the sleep habits of more than 5,000 users of a mobile phone app known as ENTRAIN.

The free app was designed by Olivia Walch, a graduate student in Forger’s group. It was launched in 2014 to help users efficiently overcome jet lag with the help of a complex algorithm based on Forger’s previous research. Essentially, the app tells people when to expose themselves to light and when to avoid it to minimize the effects of jet lag.

Entrainment is the scientific term for fully adjusting to a new time zone – hence the app’s name.

Roughly 8 percent of the app’s international users agreed to share their information anonymously, providing the team a treasure trove of real-world sleep statistics.

In a paper published Friday in Science Advances, Forger and his co-authors released their findings from ENTRAIN data.

Of all the factors considered in their analysis, gender plays the biggest role in how long a person sleeps. On average, women schedule 8.07 hours of sleep, while men schedule 7.77 hours.

On average, older people schedule sleep earlier than younger people. Also, there is less variation in the times that older people sleep then younger people.

Nationality also plays a role in sleep duration. Residents of Singapore and Japan had the shortest sleep duration of the 20 countries represented in the study.

People in the Netherlands were the most well-rested.