Some economists, such as Claudia Goldin and Lawrence Katz, trace the growing pay gap to increasing demand for skilled workers.

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Lawrence Katz, a prominent Harvard labour economist was, for a while, chief economist at the Labour Department under Robert Reich, another Harvard man.

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Harvard economist Lawrence Katz, one of the study's authors, agreed that most families in the study hadn't been able to move to better school districts, as initially hoped.

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The biggest problem areas, said Harvard University economist Lawrence Katz, are young people who haven't entered the labor force and a large number of people who have applied for long-term disability benefits after losing their jobs.

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Lawrence Katz, a Harvard economist who discussed Mr Krugman's paper at Brookings, estimates that, using Mr Bivens's approach, trade with poor countries can account for about 15% of the growth in the wage gap between skilled and unskilled workers since 1979.

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