Changes in the skill differential are often used by economic historians to proxy changes in income inequality. According to Jeffrey Williamson and Peter Lindert, American skill differentials rose sharply between 1820 and 1860, which they interpret as increasing income inequality. Using a large,...

That investment in human capital has made an important contribution to the increase of labor productivity and per capita income during the last several centuries is widely acknowledged. While much of the research on this issue has focused on education, many scholars have also directed attention...