IQ and the Wealth of Nations is a 2002 book by Richard Lynn, Professor of Psychology, and Tatu Vanhanen, Professor of Political Science. The authors argue that differences in national income (in the form of per capita gross domestic product) are correlated with differences in the average national intelligence quotient (IQ). They further argue that differences in average national IQs constitute one important factor, but not the only one, contributing to differences in national wealth and rates of economic growth. Critical responses have included questioning of the methodology and of the incompleteness of the data, as well as of the conclusions. The 2006 book IQ and Global Inequality is a follow-up to IQ and the Wealth of Nations by the same authors.