Given this debate, I wondered whether Gelman’s critique might also apply to the U.N.’s original cross-national Human Development Index, so I downloaded the latest data. The graph below compares a country’s ranking on the human development index with its ranking on average income. The correlation between the two is even stronger — a massive 95 percent! For all but a handful of countries, your ranking on average income is the same as your ranking on this multi-dimensional index.
Interesting. I'll talk about this in a moment, but first I want to address what Wolfers says about yrs. truly:
Some commentators have been comparing the scores of individual states on the state-based index with the international index, which yields newsworthy bites, like “Mississippi has an H.D.I. level roughly on par with that of Turkey.” But the two indices aren’t comparable. Dig deep into the methods used to construct the state-based index, and you’ll find that not only are the inputs different, but so are the formulae.Aha! What Wolfers is ignoring is that I was comparing fake data for the US states to real data for countries. But they were on the same scale! It was an apples-to-apples comparison - it just happens that some of my apples were imaginary.
Okay, back to Wolfers' substantive point: I believe I disagree! It is the case that his chart ends up showing a rather straight, clumpy diagonal line, meaning that most countries' ranks for HDI are quite similar to their ranks for GDP per capita. But it's also obvious that there are a handful of big outliers. GNQ appears to be ranked in the 110s for HDI but in the 20s for GDP/capita. CUB is in the 40s for HDI but in the 80s for GDP. QAT is in the top 5 for GDP but in the 30s for HDI, etc. But more than that: the general correlation doesn't seem to hold as well when you zoom in on this chart. For instance, look at the lower-left corner, where all the wealthiest and most developed countries are clustered. Within that group, there seems to be wide divergence from the overall trend that GDP/capita rank directly correlates with HDI rank. Or look farther up the diagonal line: RUS and ALB (presumably Russia and Albania) both appear to follow the general pattern of a strong correlation which Wolfers sees in this data. But RUS appears to be ranked in the 50s for GDP and in the 70s for HDI, whereas ALB look to be right around 70 for HDI, but is way to the right on the GDP scale, somewhere in the 90s. That's a significant difference!
Wolfers concludes, "For all the work that goes into the Human Development Index, it just doesn’t tell you much that you wouldn’t learn from simple comparisons of G.D.P. per capita. But you do get the veneer of something broader, with a normatively loaded name for this index." But the difference between RUS and ALB is big, and if we didn't have HDI, we wouldn't have the vocabulary (or as much vocabulary, at least) to talk about that difference. Or about the difference between a rich petro-state and a Scandinavian democracy. Or about the consequences of Cuba's form of government on its people's standard of living. All Wolfers' chart demonstrates, really, is that rich countries are almost certain to have high HDI ranks, poor countries are almost certain to have low HDI ranks, and middle-income countries are almost certain to have middling HDI ranks. But we already knew that! Wolfers doesn't acknowledge that, with only a slightly more fine-grained look at the HDI numbers, we can find a ton of valuable information that we can't get from simply looking at GDP/capita. The HDI has more than a "veneer of something broader." It gives us the vocabulary to talk about development in terms of something other than just GDP; it allows us to contribute other values to our understanding of what it means to achieve development.