[Berobero]

- Average sleep varies fairly significantly internationally (https://www.economist.com/1843/2018/03/01/which-countries-ge...), and regionally just in the US (https://www.cdc.gov/sleep/data_statistics.html)

- Average sleep is, obviously, not necessarily optimal; recommendations seem to tend towards 7+ hours on average (e.g. https://www.cdc.gov/sleep/about_sleep/how_much_sleep.html), and there's of course data to support that recommendation (again https://www.cdc.gov/sleep/data_statistics.html)

[taxcoder]

The data is interesting, but I am always skeptical of self-reported sleep times. It seems there is a sense of pride some people take in sleeping less than others.

[Berobero]

There's definitely reason to be suspect, although it looks like, on the average, it might be the reverse of what you seem to be expecting (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2785092/):

"Our model suggests that persons sleeping 5 and 7 hours over-reported, on average, by 1.3 and 0.3 hours respectively."

For self-reporting sleep studies, perhaps people have it in their head that 8 hours is how much they're "supposed" to sleep and they over-report to better match that?

Of note, however, while the CDC data I linked comes from the Behavioral Risk Factor Surveillance System which does appear to be merely a self-reporting survey question (https://www.cdc.gov/sleep/surveillance.html), the data in the Economist article comes from an app (www.sleepcycle.com). Granted, I suspect the latter almost surely suffers from some kind of non-trivial selection bias.

[jb775]

Would be interesting to look at smart watch data to see actual averages. You can tell when a person is sleeping by watching their motion activity (obviously) in combination with a drop in heart rate.