In defense of correlation/causation blowhards

Let’s get one thing out of the way first: There is not a single scientist or science journalist who doesn’t know that correlation does not equal causation. Most have probably known it since high school.


That’s why there has been a bit of a backlash against internet commenters who keep pointing it out. The phrase is “common and irritating”, writes Slate’s Daniel Engber in his article The Internet Blowhard’s Favorite Phrase. To Engber, correlation≠causation is a “freshman platitude” that professional scientists and journalists don’t need to be reminded of. Scientists are merely suggesting a causal relationship. They are not claiming it is proven.

I can see why writers and researchers find it frustrating to be scolded about something they already know. But correlation≠causation is one of those things that has a way of sliding onto the back burner of one’s mental awareness, even among scientists. On one day a research group is acknowledging the limits to their correlational study, but the next day they are advancing policy arguments that depend on a causal relationship. Or more commonly, they are preparing to run yet another correlational study.

Nowhere does this seem more of an issue than in nutrition science and in education research. In nutrition science, it is much easier to conduct a simple survey on health and eating habits than to organize a large-scale longitudinal randomized control study. Is it any wonder then, that after 50 years of nutrition science we still don’t know whether saturated fat is good for you or bad for you? And in education research, it is much easier to run a correlational study on class size and achievement than it is to run a randomized control study. Is it any wonder then, that the public policy debate about class size is so muddled?

Don’t get me wrong — There is some fantastic causal research coming out of the nutrition and education fields. And there is nothing wrong with running a correlational study either. Correlational studies are a great way for researchers to identify variables that are promising enough to investigate with causal methods.

But could it be that we have struck the wrong balance between correlational studies and causal studies? Could we be allocating too many resources towards easy but inconclusive studies, and not enough towards costly but more definitive research? I think the answer might be yes, and that internet comment blowhards are an important voice for this point of view.

5 thoughts on “In defense of correlation/causation blowhards

  1. The Cabinet Office just put out a great paper about the need for RCTs to inform public policy decisions. It’s amazing to see the outright resistance to sound logic in the name of self-preservation, but on the flip side it’s encouraging to see there are some very smart people campaigning for and carrying out RCTs around public policy proposals.


  2. I actually agree with Engber on this one. It’s not that the maxim isn’t important, and Engber doesn’t argue that. It’s just that people have latched onto it as a sort of critical thinking talisman that obviates the need for any deeper thought. There are subtleties and logic to establishing causality that get glossed over by a catchphrase. This is what Engber is alluding to, and I see plenty of the behaviour that he’s frustrated by.


    • I agree on all points. But in a world tipped too much towards correlational studies (or SEM / DCM studies that, by the way, are very assumption-dependent), the comment blowhards are pushing science in the right direction, even if those commenters are not the best critical thinkers themselves.


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