Fallacy - the Counterfeit of Argument

[Thomas Okken]

(08-31-2019 02:27 PM)SlideRule Wrote:  correlation is not causation

Almost invariably, when that line gets quoted, it is abused.

Here's my take: of course correlation implies causation! The only alternative is coincidence. In the example of the ferry ride, the data set is so small that coincidence is basically guaranteed. You can always fit a straight line perfectly to a data set consisting of two points. But the greater your data set, the less likely coincidence becomes. Which is why initial studies that show interesting results should always be followed up by more, and larger, studies.

I think what people abusing the "correlation is not causation" line often mean to say is that correlation tells you nothing about the direction of causation, as in the famous example of the correlation between owning a gold watch and being obese in 19th century England. But if A and B are correlated, and the data set is large enough to rule out coincidence, then there most definitely is a causal relationship. Whether that relationship is A causing B, or B causing A, or A and B both being caused by some other variable C, that is a different question.