The difference between first world and third world is usually defined in income per capita. This is fundamentally wrong. The sole characteristic which is always relevant in differentianting developed from developing countries, is not income per capita (however expressed: puchasing power parity, nominal GDP per capita, etc.) but the income gap between 'the rich' and 'the poor'. In all developing countries, the rich control the majority of wealth while the poor have to content themselves with the remaining wealth which is also in large part generated by serving the upper classes. my last trip to morocco made be think of this divide, as well as the divide between the urban and the rural. Taken together, the income gap and the urban/rural divide are much more direct and easy means of gauging development then all the complicated economic theories can dream up.