Racing stripes would be a better example. Though negligible, a hand out the window does have a causal impact on speed.

On the other hand racing stripes have zero impact, but do correlate to the speed of the car.

Bad example because yes it does make the car slow down.

> Putting your hand out of the window and then blocking the wind with a book doesn't make the car slow down.

Technically the book would add drag and the car would slow down but likely imperceptibly to a mere mortal

Maybe you can't stop the car that way, but if you feel that kind of wind on your hand you should worry that your car is going fast.

> As always with a lot of these: it's not saying causation.

But what they are saying is, it would be valuable if it was causative wiggles eyebrows

Last sentence of the abstract:

> Sleep regularity may be a simple, effective target for improving general health and survival.

>Putting your hand out of the window and then blocking the wind with a book doesn't make the car slow down.

...yes it does?

The study is clearly about correlation and not causation, but still the term "important predictor" keeps triggering me. People can't sleep due to stress or noise or disease (e.g. coughing), and while "predictor" seems to be normal science lingo I feel it nudges the conclusion of this study into the direction of causation instead of very clearly saying that it is pure correlation.

Nobody goes to bed and wants to wake up 2 hours later.