As always with a lot of these: it's not saying causation.
You might measure the speed of your car by putting your hand out of the window and notice that the wind force on your hand is strong when the car goes fast.
Putting your hand out of the window and then blocking the wind with a book doesn't make the car slow down.
Keyword: "associated"
EDIT: I meant to communicate that it doesn't make the car slow down as much as your hand behind and blocked by the book (feeling almost no wind), would imply.
Bad example because yes it does make the car slow down.
Original comment assumes the size of my hands is not 50m^2. Very presumptuous.
I think the point is that while it does act as negative acceleration there isn't a causal relationship with the actual speed of the car, which is mainly related to how far the gas pedal is pressed.
Drag is a causitive input to speed though.
Increase "dragForce", and the resulting car speed decreases. That is a causal input, not an association.Bertrand Russell objected to the notion of causation in the 1900s, because merely stating the updated dynamics of a system doesn't imply causation in any grand sense. Like hume, he dismisses causation, but not because of the problem of induction or anything, but because the concept seems incoherent to him. He especially emphasized this in physics - although maybe you can argue that for everyday human language, causation is good (Alice caused BCD to happen), in physics it doesn't belong.
Not that I entirely agree with his account but just some food for thought.
Initially I assumed it to be negligible but the numbers are actually very close!
I calculate around a 3% drop in speed (from 60mpg) for holding an average sized book out of the window. That's surprising to me.
It's not quite right to use hazard ratios to calculate life expectancy. But if we force it, it looks like being in the top 20% of "regular" sleepers compared to the bottom 20% confers 3-4.5 years of extra life (from birth, assuming everything else equal, assuming USA, etc.). That's 3.8%-5.7% more life (79 year life expectancy at birth in the USA as of 2025). So the numbers are actually close.
I made a bad analogy :)
But you get my point!
In this example you're determining the speed of the car based on the wind flow on your hand. Putting the book in front might slow down the car, and it will probably also slow down the flow on the hand. However, if you still try to determine the speed of the car from the air flow on the hand, you'll probably be off, because car speed and wind flow aren't linked like that when the book is in the picture.
It's a multivariate system, the dragforce is determined by the car geometry + book, hand, whatever.
They are both causes to speed.
In fact you don't even need flow to infer speed. You can just use pressure calculations and temperature, which is how airplanes measure their speed.
Controlling drag is a major component of the inputs to speed when flying an aircraft.
I can't tell if this is germane to the analogy or not, but the air flow over your hand, even behind a book, is still a function of the car's speed. As an illustrative example, imagine the feeling when the car is at 0 compared to when the car is at 60.
You think blocking the wind from hitting your hand slows the car down?
But what color is that bike shed ??? /s
Right??? The HN pissing contest...
Sorry but it's counterproductive to people's understanding of the causation vs correlation distinction to provide an example of the former and call it the latter.
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.
We could pick a company car in my previous company (it's a tax thing). We could pick any color, apart from red, because the insurance forbade it - red cars get into more accidents. Somehow that must have made it all the way to the policy without someone asking "is it the red car or the kind of person that picks a red car that causes more accidents?"
I drive a "Victory Red" 2005 Chevy Silverado. I always thought it was a "safer" color for a vehicle.
I have always assumed that, being in a larger vehicle that is bright red, people would be more likely to spot the vehicle from further away, notice it out of the corner of their eye, or that I would generally be MORE visible to other drivers.
I'm sure the correlation insurance companies are looking at is that the driver's of red vehicles are the cause of the higher accident rate.
IDK. I got a hand-me-down sporty car when I was in high school, which was initially white, then I had it painted orange as a birthday gift a year or two later. Comparing the before and after, there was a noticeable shift in how other drivers responded to me, and not universally for the better. I was less likely to go unnoticed (think people trying to merge into me, or jumping out in front of me when they have a yield), but a subset of people (mostly other young men, sometimes older men driving minivans) would act significantly more aggressively. No one ever tried to race me when my car was white. It'd happen like once a week once the car was orange. People actively speeding up to avoid me passing them also increased substantially.
The solution is clear: Offer the red car option as a trap, banning anyone who chooses it.
What about speed holes?
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.
> ... you should worry that your car is going fast.
Only if we know of an intervention that will likely slow the car down and the risks+cost of that intervention justify the benefit.
Otherwise, we worry without purpose.
EDIT: I will say that there is a philosophical question here related to "basic research" / "pure science" / "fundamental science." Usually just "knowing new things" eventually proves valuable, especially in a long timeline. So in that sense, TFA could be important.
> 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
Assume the book is the same form and size as the hand (though very thin).
> 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.
> Sleep regularity may be a simple, effective target for improving general health and survival.
But why would it NOT be? Seems stupid for us to have evolved into beings that need our sleep to be irregular.
There are things that are causal and have little to no effect and things that are causal and have a large effect. I think determining whether and how much something matters, especially when the target audience is "all humans" is a worthwhile endeavor. So it may seem obvious to you, but many many important scientific findings were because somebody looked a little deeper at something that seemed obvious to everyone else.
Because for it to be effective it must have reasonable cost compared to the benefit. The cost for such a sweeping lifestyle adjustment seems quite high, and the authors have not showed any benefit to interventions.
>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?
only if the book is being held by someone in the car.
Presumably, the example missed the part where they stated the book was being held in front by an outside agent, because that is the only way it would make sense.
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.
But they choose to. Alcohol, caffeine in the afternoon, just not realizing blackout curtains matter, lights or displays on in the room... you can't help someone who isn't making bad choices, but most people can make simple choices that improve their sleep a lot!