Reading this discussion by Matthew Yglesias about purchasing power parity adjustments reminds me of the time I tried to track down Russia’s per-capita GDP. I got the following different numbers:
$7,600 (World Bank 2007)
$9,100 (World Bank 2007)
$14,700 (PPP adjusted, World Bank 2007)
$4,500 (World Bank 2006)
$7600 or $14,400 (gross national income: “Atlas method” or “purchasing power parity,” World Bank 2007)
$12,600 (IMF 2008), $9,100 (World Bank 2007), or $12,500 (CIA 2008)
$2,637 in 2000 US dollars (World Bank 2007); that’s $3,200 in 2007 dollars
$2,621 (World Bank 2006) or $8,600 (IMF)
Various commenters patiently explained to me about PPP adjustments, but, as I wrote at the time, I was surprised the numbers varied so much. I can accept that the PPP adjustment can make a big difference, and I know that exchange rates fluctuate—but varying from $2600 to $14000? That’s enough variation that I don’t know what to do with these numbers at all. In any particular analysis it makes sense to get all your numbers from the same source, but maybe not to take these numbers too seriously.