[nosefurhairdo]

The person I responded to (correctly) criticized per capita GDP, citing differences in cost of living. I felt that referencing PPP would be helpful since it attempts to factor in cost of living differences.

I'm not sure this "comparisons are hard" speech is adding much. Differences in wealth are real, measurable, and meaningful, even if they can't be boiled down to a single number. Obviously there are other factors to quality of life; nobody here stated anything to the contrary.