The present note raises the issue of how best to interpret the World Bank's (WB) much used "constant USD per capita … income" concept and similar series. We find that the guide to its construction appearing on the WB data portal to be sketchy …

capita income. International trends of life expectancy and per capita GDP differed during the past 150 years. Life expectancy … expectancy and per capita income and its outward shift over time as put forward by Samuel Preston. However, the association … between non-linearly transformed life expectancy and the log of per capita income does not flatten out over time, but becomes …