Dubious data cut down to size
By Tim Harford
A doctoral student found that national income is correlated with the average length of the erect penis in a country
THERE'S NO DOUBTING THE smash-hit economics research paper of the summer. It is “Male Organ and Economic Growth: Does Size Matter?”, a working paper written by Tatu Westling, a doctoral student at the University of Helsinki.
Let’s get the conclusions of the article over with first, because there is a serious lesson, somewhere. Westling discovers that national income is correlated with the average length of the erect penis in a country. Specifically, medium-sized erections are correlated with the highest national income (in 1985, as it happens) and small erections are associated with economic growth between 1960 and 1985.
To reach his conclusions, Westling performed a statistical technique that is known in the trade as a “cross-country growth regression”. Beloved of (some) development economists over the past couple of decades, it has been made possible partly by computers. But its deployment depends mostly on the careful cultivation of data sets describing GDP, political system, educational attainment and other variables, for large numbers of countries over many years. You throw the numbers into the computer and see which features of a country’s economy are correlated with economic growth. Westling simply added some rather unconventional data.
This strategy has produced many answers – rather too many, in fact. In 2002, the development economist Romain Wacziarg wrote, with a touch of acid: “the list of proposed panaceas for growth in per-capita income has included high rates of physical-capital investment ... low fertility, being located far from the equator, a low incidence of tropical diseases, access to the sea ... and suitably conditioned foreign aid.” I have omitted 17 of Wacziarg’s “panaceas”, and he pointed out that the list is “growing and non-exhaustive”. To it, we can now add erect penis length of 13.5cm – what Westling has demonstrated is “the GDP maximising size”.
Westling claims that he uses standard statistical methods and that his results are robust; that the correlation is both highly statistically and economically significant – in other words, the result is big enough to matter (please – no giggling) and is unlikely to be a coincidence.
Well, well. What are we to make of this? I asked Westling how he would characterise his research paper, and he suggested the term “sardonic economics” – and, he added, “Scientifically, this paper is probably as worthless as much of contemporary economics.”
Westling is a little too harsh, but only a little. Cross-country growth regressions have been used to demonstrate a vast number of statistical relationships, some mutually contradictory. (Particularly notorious is the vast and unfulfilling literature showing that foreign aid increases growth, or does not increase growth, or leads to growth under certain conditions.) Such regressions are not compelling, because the number of different statistical relationships that might be tested is truly vast, and the data themselves are sometimes sketchy. (Although few data sets are as of dubious a provenance as Westling’s data on penile length, a fact he cheerfully acknowledges.)
Cross-country growth regressions have their uses, given a sense of perspective about how fragile their results can be, and how difficult it can be to turn a statistical correlation into a workable policy. But if you are wondering how much weight to place on a statistical technique that can produce a robust connection between the size of a penis and the size of an economy, you are right to do so.
Unless, of course, the apparently ludicrous relationship is real? I asked Westling about this. “One biologist suggested to me that testosterone might explain something,” he responded. I doubt it.
Tim Harford’s new book is ‘Adapt: Why Success Always Starts With Failure’ (Little, Brown)
Copyright The Financial Times Limited 2011.