Which nation produces the richest people in the world? You might think that an easy question to answer: just grab the latest figures from the International Monetary Fund, and you’ll see that the answer is Luxembourg ($102,000 gross domestic product per head in 2007). The US is in ninth place ($46,000) and the UK in 11th ($45,000).

There are some methodological wrinkles to iron out: what exchange rate to use, for instance. And for the poorest countries such as Liberia ($200 per person in 2007) or Burundi ($130), the numbers involve some guesswork. But overall, these are not controversial statistics – unless you are Lant Pritchett or Michael Clemens.