The amount of mozzarella cheese consumed annually in the United States appears closely correlated with the number of doctoral degrees in mathematics awarded each year. Do newly minted math professors consume large amounts of pizza, and consequently of mozzarella cheese? Or does mozzarella make people better at math generally, and therefore more likely to finish their dissertations in a given year? Both explanations seem unlikely.
This chart is taken with permission from Tyler Vigen’s Web site, an ingenious project that automatically seeks correlations between unrelated data series.