Krugman’s Explanation of Stagnant Real Wages

On the run today -- guests arriving soon and I am nor yet ready -- so some quick ones. This one came by email from Fred Moseley, and I haven't had a chance to give it much (i.e. any) thought. Comments?:

Krugman’s explanation of stagnant real wages: In a recent post on his NYT blog (“Technology and Wages”) Paul Krugman argued that the reason for stagnant real wages in the US economy in recent years is that technological change has been “capital-biased”, in the sense of Hick’s “capital using” technological change. Unfortunately, Krugman did not explain clearly what he means by “capital biased technological change” (as several readers complained).

According to Hicks, capital-using technological change (i.e. Krugman’s capital-biased) increases the marginal product of capital faster than the marginal product of labor (i.e. ↑MPK > ↑MPL). Krugman concludes that “we’re seeing new technologies that look, on a cursory overview, as if they’re capital biased.”

My question to Krugman (if I may) is: how do you know that technological change has been “capital biased”? A “cursory overview” of what data? What is the empirical evidence for this conclusion? How are the MPL and MPK estimated, independently of wages and profit? I know of no way to do this, especially for an aggregate production function.

Furthermore, the MPL (or MPK) is a logically incoherent concept, because the MPL (a partial derivative of the production function) requires that labor be increased by one unit and all the other inputs be held constant. But that is not possible in all goods-producing industries – it is not possible to increase labor and output without at the same time increasing raw material inputs (and other intermediate inputs); e.g. it is not possible to produce another shirt without more cloth, and not possible to produce another car without more tires, brakes, etc. If a firm hired labor up to the point where the real wages = MPL, it would lose money, because it would not have taken into account the extra cost of additional raw materials and other intermediate inputs. This non-existence of marginal products is not widely recognized, but it should be.

Another reader made a similar criticism: “The argument depends on the theory that workers are paid their marginal product. Some people hold to this old idea, however it is not supported by the empirical evidence.” Amen.

For further discussion of criticisms of marginal productivity theory (a two part paper), see here and here.

It is time we stop talking about marginal products and look for other better, logically consistent and empirically supported theories of the distribution of income.

I agree with Krugman in a subsequent post where he stated: “If you want to understand what’s happening to income distribution in the 21st century, you need to stop talking so much about skills, and start talking much more about profits and who owns the capital.”.

But marginal productivity theory is not a coherent way to talk about profits.

Fred Moseley
Mount Holyoke College