HERE is a shaming statistic: divide the US by race, sex and county of residence, and differences in average life expectancy across the various groups can exceed 30 years. The most disadvantaged look like denizens of a poor African country: a boy born on a Native American reservation in Jackson County, South Dakota, for example, will be lucky to reach his 60th birthday. A typical child in Senegal can expect to live longer than that.

America is not alone in this respect. While the picture is less extreme in other rich nations, health inequalities based on race, sex and …