Understanding why some countries are poor and why some grow than others is probably one of the most important questions in Economics. The traditional tool to tackle this challenge has been growth regressions: use cross-country data and regress the GDP growth rate on various indicators that could be relevant in order to find which matter most. These regressions have been abused over the years, especially as there are obvious endogeneity and collinearity issues. Also, the results are driven by a multitude of (poor) countries where data quality is quite horrendous. The worst is probably all the data mining that is going on in this literature, which culminated with Xavier Sala-i-Martin's two million regressions.
Tatu Westling uses a variable the previous literature completely ignored: the average length of the erect human penis. Adding this variable to the regression shows a U-shaped relationship for the GDP level, explaining 15% of its variation. The optimal penile length is 13.5 cm, and 16cm is disastrous. For GDP growth, the relationship is negative, explaining 20% of the dispersion. This is not negligible, and more than institutional variables that are thought to be the key to growth and convergence.
I wonder how many people will take these results seriously and try to get policy recommendations from it. Westling hypothesize about the impact of self-confidence. The paper is very well written, taking the 'male organ hypothesis' very seriously, but in truth tongue-in-cheek. Very different from this study on flag colors I wrote about previously.