The UNDP's favoured measure of progress throws up some intriguing comparisons

GROSS domestic product, Robert F. Kennedy said, “measures everything…except that which makes life worthwhile.” In an attempt to redress the fixation with economic output alone, in 1990 the United Nations Development Programme (UNDP) launched the Human Development Index (HDI). This index combines life expectancy at birth, the average and expected number of years in education and economic output. Only two countries, Zimbabwe and Lesotho, have seen their index scores fall since 1990, but elsewhere big strides have been made, particularly in China, Iran and India. As a result of these changes, the UNDP expects the world’s middle-class population—defined as households with incomes over $20,000 a year—to grow from 1.85 billion in 2009 to 3.25 billion in 2020. It predicts that by 2030, 80% of middle-class households will live in emerging and developing countries, accounting for 70% of global spending.

These figures mask some important difference within countries. The UNDP estimates that Latin Americans in America have an HDI of 0.75 (on a par with Kazakhstan). African-Americans have an HDI rating of 0.70, which is similar to China's. African-Americans in Louisiana score just 0.47 (equivalent to Nigeria).