Sleep 7 hours or more per day and you die early

This seems to be an unscientific conclusion. There's no mention of other conditions the patients may have had or acquired before the follow up and how those conditions may have played a part in their sleep habits and/or lifespan.<p>It's like saying, "a random sample of the population showed that people who take insulin are found to be at higher risk for glaucoma." Of course they are, because people who take insulin are probably diabetic, and glaucoma is a common complication of diabetes. That doesn't mean taking insulin causes glaucoma.

I simply do not know how one concludes that sleep, among all other things, is the reason for the deaths? When studying humans, how do you account for all the other lifestyle variables?<p>Does anyone on HN do these types of studies and can comment? Seems so very unscientific.