Thanks to Kristine, I really shouldn’t need to translate this Norwegian blog post, but for future reference:

As any statistician worth his or her standard deviation is well aware, covariation does not mean causality – or, in more civilian terms, just because something moves at the same time or later than something else, the first does not necessarily cause the other.

Otherwise, it would be really easy to explain global warming: Baby boomers reaching menopause.

But how to explain this to students? I use this drawing by the Swedish genius caricaturist, Albert Enström (1869-1940):

In English, the caption is During a convivial gathering there is talk of the unhygienic aspect of using galoshes. One of those present chips in: "Yes, I’ve also noticed this. Every time I’ve woken up with my galoshes on, I’ve had a headache."

That’s all. We will now return to our usual programming.

Updated: Boingboing!