1. Knowing what country an individual lives in explains about 70 percent of the observed variation in income across individuals (p.11).
2. If we could magically eliminate all income inequality within nations, the world’s total income inequality would shrink by at most one-third. Most of the relevant inequality is across different nations (p.11).
3. Global income inequality is falling, contrary to what many critics charge (pp.17-18). So the world’s poor are catching up to the world’s rich (p.18), on average.
4. Most poor countries are not catching up, most of all Africa. The world’s poor are catching up, on average, once we weight countries by population. The growth of China, and to a lesser extent, India, has driven the improved prospects of the poor and the decline in cross-nation inequality (passim).
5. If we compare the United States to Western Europe, there is considerably less inequality within the United States.
As you might surmise, I found this book to be excellent and highly instructive. It reads more like an extended article than a book, but nonetheless it delivers on the substance.
Addendum: Daniel Drezner offers some interesting remarks, with links, on Paul Krugman’s recent writings on inequality.
Subsequent addendum/clarification: Firebaugh (p.193) writes: “average income is much more unequal across nations in Western Europe than across states in the United States.” He does not (and could not) argue that “within a single nation equality” is less in Europe. Here are Gini coefficients for the various European nations and the United States.