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Klass13 t1_je5zr1v wrote

I've heard this but not entirely how it would work, care to elaborate? Is it because there may be another different variable which cancels out the causality effect leaving non observable correlation?


compounding t1_je6a9wj wrote

That’s one case, yes. Think of a situation where the causal effect is only responsible for a small portion of the observed outcomes, so the gross correlation could even run backwards due to other factors despite known causation in part of the sample.

Or there could be other causal factors stemming from the original cause that push back the observed correlation which need to be accounted for. Certain genes are known to cause breast cancer at such a high rate that everyone who screens positive for them might choose to get double mastectomies, causing breast cancer rates to actually fall among that group. I don’t think this is actually true, but it’s a hypothetical example of a case where no or even reverse correlation might exist despite known and strong causation.


Klass13 t1_je6ro8m wrote

That's amazing, thanks! Do you happen to know any good subreddit about stats and whatnot?


compounding t1_je7g0uy wrote

Not in particular to stats, no, but I also haven’t really looked for something like that.

Maybe the only place I know that might have a higher than usual concentration would be /r/slatestarcodex, which has some small overlapping interest in Bayesian reasoning and is generally more interested than other communities in using stats accurately rather than just as a tool to prove pre-determined point (sometimes).


SerialStateLineXer t1_je83s9x wrote

People who take antidepressants are more depressed than people who do not. If we just look at the correlation, we might assume that antidepressants cause depression, but the opposite is true.

In this case, there's still a correlation, but the sign is the opposite of the true causal effect of taking antidepressants.

Alternatively, consider a car being driven over a hilly road at a constant speed. When the car is going uphill, it's burning more gas. There's no correlation between speed and gas consumption, but gas consumption increases speed.