This article is from the archive of our partner .

The opening question to most undergraduate macroeconomics courses usually is, "Why are some countries rich and others poor?" The lecturer will then probably dive into all of the usual suspects behind economic growth--natural resources, technological innovation, savings rate--without mention of perhaps the most primal of measurements: penis size.

That's right, penis size. In a study published today, the University of Helsinki's Tatu Westling points out a surprising strong correlation between a country's GDP growth rate and average penile length. As the chart above shows, countries that averaged smaller penis sizes grew at a faster rate than their larger counterparts between 1960 and 1985. Every centimeter increase in penis size accounted for a 5 to 7 percent reduction in economic growth. The study also showed that overall GDP was at its highest in countries with average-sized penises with GDP falling at the extremes of penis length.

As Westling explains in his paper, previous studies "concentrate on economic, social and political factors, these and many related treatments largely abstain from biological and/or sexual considerations. The aim of this paper is to fill this scholarly gap with the male organ." Interesting choice of words (the study is full of them, as you'll see below), but why should this particular, um, unit have any explanatory power? Penis size and economic growth might be related through some intermediary variable like gender equality, political stability, or population growth, Westling writes, but he seems to prefer an admittedly more Freudian explanation that goes like this: Penile length and income are both factors that contribute to an individual's level of self-esteem, and if a person has more of the former, he'll need less of the latter. Or, to put it in layman's terms, some fast-growing countries may be compensating for something. Not a particularly poor argument until you realize, as Westling acknowledges, that half the world's population don't have penises.