In 1992, a publication appeared in the British Medical Journal written by Richard Wilkinson, featuring a simple graph of life expectancy in 1981 among nine rich nations, along with the percentage of income received by the poorest 70% of families for each country. It showed how greater inequality in a country was associated with lower life expectancy, with only a weak link between national incomes and mortality rates. Richer countries were not necessarily healthier than less rich ones, at least among developed nations. Increases in income inequality over time were linked to higher death rates. But were the results valid?

Depending on a single study as definitive evidence is a shaky way to stake a claim. Knowledge progresses by conjectures, critical commentary, discussions, and either general acceptance or rejection. Yet five previous studies, beginning in 1979, demonstrate similar findings. In 1996, two studies from University of California and Harvard reported the same […]