There is a story to the effect that a statistician once found a very high correlation between the number of old maids and the size of the clover crop in different English counties. After puzzling over this relation for some time, he was able to trace what appeared to him to be the causal chain. Old maids, it appeared, kept cats; and cats ate mice. Field mice, however, were natural enemies of bumblebees, and these latter were, in turn, the chief agents in fertilizing the flowers of the clover plants. The implication, of course, is that the British Parliament should never legislate on the subject of marriage bonuses without first evaluating the effect upon the clover crop of reducing the spinster population.

— Herbert Simon, Administrative Behavior, 1997