The useage you cite, ‘Correlation does not imply causation.’ seems quite wrong. It seems obvious to me that correlation *does* imply causation – but it doesn’t prove it.

Spurious correlations can be quite fun though 🙂

Brett, that’s a possibly correct post hoc explanation but usually does not apply. Most of the time the conversation is not about experiments at all. Correlation doe not suggest uncontrolled variables at all; in a very large number of cases, with high correlations, it would be wrong to assume that there are. So-called “causational methods” don’t so anything to identify cause. Having a high correlation and an excellent understanding of physical causality for a system does not get better by using “causational experimentation” which is little more than normal experimentation where you’ve made explicit statement about cause. Finding a correlation between two variables by surprise provides only weak suggestion of an underlying cause. For this reason, the only real difference between an approach that is “correlational” and one that is “causal” is the level to which one argues against a proposed cause on the basis of a prior incredulity. That is rarely helpful or impressive.

So no, that’s not what it means, not where the term comes from, or how it is ever used except in a few rare instances, and the distinction between correlational and causal (the latter only used in some subfields but with analogs elsewhere) is not a novel experimental or statistical technique, really, but an approach to structuring analysis, which still requires understanding of (and proof of) mechanism.

But you can never “prove” casuation. You can increase confidence in your hypothesis, but you will never reach 100%, no matter how much research you do.

You can’t prove causation because it can never be observed. Even in the case of the apply and gravity mentioned in the blog, we can’t be 100% sure that gravity caused the apple to fall. It’s possible that one day an apple might shoot sidewards instead of falling; it’s possible that that might already have happened, but no-one saw it.

To prove casuation, you’d have to be omniscient; and we’re not.

Pointing out smugly that “correlation does not imply causation” is incessant on science forums. We see that comment, and cringe, as it is clearly degrading to people that found correlation and want to continue along with the research until they prove causation, or their theory disproves itself.

It is nauseating to read comments constructed by mental midgets disparaging epidemioligists, statistical analysts, herpetologists, and world renowned disease control scientists with an obscenely misused phrase like “correlation does not imply causation”. Save your flimsy knowledge of statistics and science to impress the freshmen during frosh week.

The original problem comes from the use of the word “Imply” in logic vs. “Imply” in vernacular parlance. Like the word “Theory” in science vs. the vernacular they are almost opposites. I imply things in my daily speech that I’m trying to avoid saying, sometimes because I can’t really say it. A implies B in logic because if you see A you should bet on B.

Is Gravity “our” explanation for apple falling or did it really “cause” the falling?