People in Singapore and Japan get the least sleep, while the Dutch and New Zealanders sleep the most, according to a new sleep study published last week in Science Advances. While the insights about different countries are interesting, the most compelling thing about the study of more than 5,000 people was that it used a smartphone app to study people's self-reported sleep habits in the real world, rather than in a lab. In doing so, researchers managed to challenge some widely-held ideas about sleep.

Researchers from the University of Michigan, Ann Arbor created an app that would provide users with a service in exchange for their sleep data. The app, called Entrain, recommends optimal lighting conditions for jetlagged travelers adjusting to new time zones. Users opt in to submit data about their normal (non-traveling) sleep habits. 

Laboratory tests have generally shown that factors like age, sunrise time, and sunset time all affect sleep by affecting the time a person wakes up in the morning. But the Entrain study showed that home country (which the researchers used as a proxy for social factors) affected not wake time, but bed time. Generally, those in countries that got more sleep also went to bed earlier, but they didn't necessarily wake up earlier or later.

"This points to the hypothesis that biological cues around bedtime are either weakened or ignored for societal reasons, thereby leading individuals to delay their bedtime and truncate their sleep duration as a result," researchers wrote.

The data had a few other interesting insights as well. Women in general slept more than men, going to bed earlier and waking up later. Users who reported being exposed to natural, outdoor light during the day tended to go to sleep earlier and sleep more than those who spent most of their day in artificial lighting. Finally, age had the biggest effect of any factor on sleep timing.

There were some caveats on the data. The process researchers used to eliminate outliers also likely eliminated any shift-workers or others with highly atypical sleep schedules from the study. Also there was an inherent bias toward smartphone owners and those likely to do international traveling, and thus need an app for mitigating jet lag.

Nonetheless, researchers celebrated the data collection potential of a mobile app, and noted that even better results could probably be obtained with wearables, which could record sleep times automatically, and thus more reliably, than self-reporting.

"[W]e use mobile technology to collect a massive data set at essentially no cost," researchers wrote. "Advancing technology and wearables will soon increase the already substantial amount of human data available and will enable us to gain further insights into the toll that sleep deprivation is having on the population."