Comment by abdullahkhalids

The confounding variable I think is most important is that many people have an internal clock that is shifted or lengthened relative to other people in the same house.

If others in the house prefer to sleep from 10-6 and you prefer to sleep from 12-6, but others start making noise a 6, your sleep quality in the last two hours is destroyed. Then over time, it just results in poor sleep regularity, as you cycle between exhaustion and trying to sleep according to your internal clock.