# How does daily amount of sleep vary within and between healthy adults?

I'm interested in research that has employed the following or similar research design:

• Measure the daily amount of sleep
• every day for an for an extended period (e.g., more than a month)
• in a relatively large sample (e.g., $n > 100$) of "normal" healthy adults

This would give rise to sleep measurements on multiple days and for multiple individuals. Thus, we could define $y_{ij}$ as the amount of sleep of person $i$ on day $j$. Descriptive statistics could be calculated on the set of daily sleep measurements of person $i$ such as the mean and standard deviation. These within-person descriptive statistics could also be summarised at the group-level.

### Questions

In general, what are the main descriptive statistics of such data?

More specifically, I'd be interested in knowing:

1. What is the mean of the within-person mean of daily amount of sleep?
2. What is the standard deviation of the within-person mean of daily amount of sleep?
3. What is the mean of the within-person standard deviation of daily amount of sleep?
4. What is the standard deviation of the within-persons standard deviation of daily amount of sleep?

Presumably such results are contingent on how sleep is defined and measured, as well as many other factors such as the nature of the target population. Thus, any comments about these factors would also be welcome.