adam smith amartya sen atkinson index david ricardo decile distributive justice economic growth economic inequality economic policy factors of production foster greer thorbecke gini coefficient harvard university hoover index human development index income income inequality in the united states information theory international inequality kuznets curve list of countries by income equality lorenz curve median metrics millennium development goals pareto principle poverty redundancy robin hood index socioeconomics systems of measurement the rich get richer and the poor get poorer theil index thomas malthus world bank