Hacker News Reader

Comment by calibas | Hacker News Reader

I don't get this attitude, if things are correlated, it should at least make a scientist wonder why. It certainly could be random chance, but correlation can also lead to establishing a causal model or discovering a third variable. If two things keep happening in conjunction, it at least merits further investigation.

It seems like there's this extreme reaction against people behaving like correlation equals causation, but instead of over-emphasizing correlation, it gets dismissed entirely.

View on HN

Yes, the classic example being the connection of lung cancer to smoking. Initially it was just a correlation, but the correlation encouraged scientists to see if there was actually a causal relationship (which of course there was). Yes, many (probably most) correlations are spurious, but the existence of a correlation is very useful for scientists looking to find a hypothesis to test.

I share this criticism. It's almost like you have to scream at people that although correlation doesn't imply _direct_ causation, it most certainly does imply some causal chain.

Ruling out chance through significance and power, what phenomenon in the world is correlated without being causally related _somehow_?

Well, it can also be pure randomness

They did say “ruling out chance”.

Take the worst intersection in the country this week for traffic accidents. Close the roads to the intersection at 3am and organise a contemporary expressive dance performance to rid the intersection of its evil and re-open it 30 minutes later.

Repeat every week with the worst traffic intersection for accidents.

What you find is. IT WORKS! HURRAH! These intersections are more than usually not the worst the following week! The evidence is clear. The correlation is utterly compelling. It is significant. It has power. How could it possibly be unrelated?

Now if we stop it being comically silly in our example and make it a red light & speed camera, see how the issue is much more difficult. There is a clear line of potential causation of fixing dangerous intersections. But is it really better than folk dancing for 20 minutes at 2am? [1]

[1] This example should not be interpreted as being an opposition to all red light and speed cameras.

There is a scale of certainty with causality. Evidently we aren't always good at expressing the difference between light evidence of causality and heavy evidence of causality. Do we have the right words? Are we using them?

So in other words, several of the commenters here are right. On the one hand we shouldn't jump to conclusions, but on the other hand we should listen to the clues.

Consider that we can’t even truly conclusively identify true causation using scientific experiment alone. Correlations and conjectures is ultimately all we have.

Nevertheless, the fallacy is so commonplace. You will easily find a seemingly educated person selectively balking at the notion that causal relationship is ultimately a conjecture or at the notion that causal relationship is possible, depending on their pre-existing beliefs.

Being emotionally attached to purported causal relationship X->Y, they will count all correlational evidence in favor; when pointed out that the evidence is correlational, they will wave it off with more correlational evidence.

If that causal relationship does not happen to align with their world view, of course, they will be right onto you with the old correlation-does-not-imply-causation mantra.

> if things are correlated, it should at least make a scientist wonder why

There's billions of possible variables. There's N^2 possible pairs of variables. It's not feasible to look at every pair that is correlated.

> if things are correlated, it should at least make a scientist wonder why

Not really.

See: https://www.tylervigen.com/spurious-correlations

You should still be curious as to why those correlations exist. It's still important even when the reason is p-hacking, since then you can identify dubious statistics.

yep, once in a while, it will end being a once in a life discovery.

so, everything defying common sense should be reviewed, to find why and how exactly is this happening.

I don't remember who said that (pretty sure that it was R Monroe in xkcd, as usual): correlation is not causation but the data is heavily winking at you (it was more funny in his words)

Of course it was xkcd: https://xkcd.com/552/. The exact text is: "Correlation doesn't imply causation, but it does waggle its eyebrows suggestively and gesture furtively while mouthing 'look over there'."

Reply on news.ycombinator.com