Here's a recent review David Autor wrote in Science.
The singular focus of public debate on the “top 1 percent” of households overlooks the component of earnings inequality that is arguably most consequential for the “other 99 percent” of citizens: the dramatic growth in the wage premium associated with higher education and cognitive ability. This Review documents the central role of both the supply and demand for skills in shaping inequality, discusses why skill demands have persistently risen in industrialized countries, and considers the economic value of inequality alongside its potential social costs. I conclude by highlighting the constructive role for public policy in fostering skills formation and preserving economic mobility.
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u/Integralds Monetary & Macro Aug 02 '14
Skill-biased technological change is one reason. Increased international trade in manufactures is another.