Eating chocolate makes a country produce more Nobel laureates.

In a genuine (and tongue-in-cheek) New England Journal of Medicine article, Franz Messerli (2012) plotted national chocolate consumption against Nobel prizes per capita and found a strikingly strong correlation. Switzerland topped both lists. The paper was widely reported, sometimes credulously.

The point was the opposite of the headline. It is a textbook example of an ecological correlation and the confusion of correlation with causation: wealthy countries tend to consume more chocolate and also to fund the universities and research that win Nobel prizes. The chocolate is a marker of national wealth, not a cause of genius, and comparing countries (not individuals) invites this kind of spurious link. As a causal claim, 'chocolate makes nations smarter' is refuted — and instructive.