My irritation w/Chang has nothing to do with his lack of familiarity with orthodox economics, nor did I make any inference about his intelligence or learning in general. Nor would I ever as far as inequality measures go. Chang's problem is that his e-mail only works in one direction.
I personally couldn't care less about the Gini index, the Suits index, or whatever. I never use them. There is a small academic subculture around them which accomplishes the feat of making something important very boring. Nobody really needs to know about this stuff. If you want to talk about inequality, median incomes and wages, assorted poverty measures, or simple tables about how much dough the top x get (or have) versus the bottom Y are perfectly suitable for political discourse. I am confident that a public statement to the effect that the Gini index got worse by x this past year would not have the slightest political effect.
If you want an illustration of how to use such measures, take a gander at State of Working America, which my shop puts out. No I don't receive any commissions. I don't even make any money from my own books, let alone someone else's.
What is much more important than these numbers is the answer to the following question, IMO: in what way do people care about these numbers? Since I raised it, I'll reveal my own unproven hypothesis: people in the U.S. don't give a damn about inequality. They have some concern about poverty -- particularly avoiding it themselves -- and they have certain expectations for themselves in terms of standard of living. When these expectations are dashed, they are susceptible to radical analyses of inequality and other political arguments, but as a popular issue it is very limited. Most people don't think there's anything wrong with being rich. Committing crimes for the purpose of getting rich or staying rich are another matter. that's one of our openings, since the two (crime and wealth) are often associated.
mbs