The Spirit Level revisited
As shown in The Spirit Level, this is the relationship between income inequality and life expectancy. There is a modest (r2=0.20) correlation, with the less equal countries appearing to have shorter life expectancies.
But, as I said in my rebuttal, the data used by Wilkinson and Pickett for this graph were peculiarly old. Indeed, I got my first hint that all was not as it seemed in The Spirit Level when I turned to the references and noticed that the authors used life expectancy figures from a 2006 report for one graph but used figures from a 2004 report for the graph shown above. Using the more recent figures weakens an already weak relationship, but a more fundamental problem was the exclusion of several countries from their analysis. Wilkinson and Pickett provide a justification for only studying rich countries in The Spirit Level, but there are a number of rich countries that are needlessly excluded. When those countries are added and the data from the 2006 report used, a rather different picture emerges, as the graph below shows:
Since it’s been five years since my rebuttal was published, I decided to look at the most recent life expectancy stats and see how The Spirit Level was holding up. The results are interesting. Even if you limit the analysis to The Spirit Level‘s questionable group of countries, the association with inequality has completely disappeared (r2=0.02). This remains true if you include the countries added above and if you use different measures of inequality.
It seems that the relationship between inequality and life expectancy only holds when we use data from early in the last decade and arbitrarily exclude a number of countries. It fails the basic scientific test of reproducibility. A law that only works under certain circumstances and in certain years is no law at all.
The fact that a correlation no longer exists even when we confine the analysis to the countries that were specially selected in The Spirit Level does not leave much wriggle room for the book’s authors. It is difficult to exaggerate to importance of the supposed link between life expectancy and inequality to The Spirit Level‘s argument. Richard Wilkinson made the health-inequality hypothesis his own in the 1990s, with the other connections made in The Spirit Level following on from this ‘discovery’. More than ever, that discovery looks like fool’s gold.
Christopher Snowdon is the IEA’s Director of Lifestyle Economics. He is the author of The Spirit Level Delusion.