They aren't represented on the low density countries though. In any case the point is population density is probably not the main cause. Lack of education and freedom tend to be more important. Of the ten highest PCI countries all but Singapore and oil rich countries are also free countries and all have a decent education system. Of the bottom ten none are free countries and none have modern education systems. https://en.wikipedia.org/wiki/List_of_countries_by_GDP_(PPP)_per_capita Of the lowest 10 PCI the highest population density ranks 30th on the list of countries , Burundi, the rest are considerably lower. the next is Togo at 99.City-states are over represented on the list of densest countries, so that end raises skepticism.