Matt Stoller offers this excellent presentation of the commonly used fallacy of confusing correlation for causation:
For years, we’ve been told that while drinking too much is bad for your health, having just a glass of wine with dinner, as the French do, can be good for your heart. And many studies do indeed show such an association. But what we’re discovering is that this correlation is an illusion. In fact people who drink a small amount of wine every night are healthier, but only because it means they aren’t drinking soda. Even small amounts of alcohol are bad for you, but as academics are coming to understand, if you drink a glass of wine every evening, you also tend to exercise, eat fruits and vegetables, and refrain from smoking. And it is those habits, not the wine, that improve health.
This logical fallacy is known as confusing correlation with causation, or assuming that because A happened and then B happened, that A caused B. The media loves these kinds of associations, because they seem correct, but they are often just coincidence, or a result of a variable that’s not being observed. Sometimes correlations are silly, like saying that “there are more sick people at hospitals, therefore hospitals cause sickness.” They can even be ridiculous; one famous study found that shark attacks are common on beaches with more ice cream sales, the theory being that sharks like to eat people full of ice cream.
Every aspiring law student encounters this fallacy; it’s fundamental in law to understand when something is causal vs coincidental or associative. It’s such a commonly taught error to avoid that it was the basis for one of the first episodes of the famous show The West Wing, an episode named “Post Hoc, Ergo Propter Hoc” after the latin phrase describing this fallacy. Lawyers understand the difference between correlation and causation. So do academics. An entire generation of would-be lawyers who watched the West Wing understand it. It’s not a mystery.
