Krugman’s conundrum

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: Institute, a Washington, DC, think-tank, did just that and found that trade widened wage inequality between skilled and unskilled workers by 6.9% in 2006 and 4.8% in 1995. But even with that increase, trade is still far from being the main cause of wage inequality. 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.

Even this is almost certainly an overstatement. Many imports from China have moved up-market from easy-to-produce products, such as footwear, to more sophisticated goods, such as computers and electronics. As a result, to use economists’ jargon, the “factor content” of American imports—in effect, the amount of skilled labour they contain—has not shifted downwards. Mr Katz says factor-based models suggest trade with poor countries explains only 5% of rising income inequality.

Mr Krugman argues that the effect is bigger, but that import statistics are too coarse to capture it. Thanks to the fragmentation of production, Chinese workers are doing the low-skill parts of producing computers. Just because compu- ters from China are classified as skill-intensive in America’s imports does not prevent them from hurting less-skilled American workers. Mr Krugman may be right but, as he admits, it is hard to prove.

Blame it on the rich

Robert Lawrence, another Harvard economist, has looked at the same evidence and reached rather different conclusions. In a new book, Blue Collar Blues, he points out that the contours of American inequality sit ill with the idea that trade with poor countries is to blame. Once you measure income properly, the gap between white- and blue-collar workers has not risen that much since the late 1990s when China’s global integration accelerated. The wages of the least skilled have improved relative to those in the middle. Some types of inequality have increased, notably the share of income going to the very richest. But there is little sign that wage inequality has behaved as traditional trade theory might suggest.