Comment by mewpmewp2

What I wonder is even if they did the perfect adjustments, what would have been driver for different sleep regularity.

E.g. considering some common causes like work stress - if they did the causation and compared people who did the same type of work, and they controlled for stress levels then why did one group of people have sleeping regularity issues more than compared to others?

Like there has to be some other driver then that they didn't control for, as in personality, environmental or physical difference?

Most people do want to have healthy sleep, the ones who don't usually have something causing those issues.