ROBERT FOGEL, a Nobel-winning economic historian and pioneer in the use of quantitative methods in economic history, has died at the age of 86. The University of Chicago has an obituary here, and the New York Times here. Mr Fogel was perhaps best known for his work on the economics of slavery (there is some discussion of this here). His work argued that southern farms were highly productive and profitable under slavery, and that without political change the slave system would probably have continued. My first exposure to Mr Fogel's work came as an undergraduate economics student, when a professor gave me his 2000 book "The Fourth Great Awakening and the Future of Egalitarianism". It is a thought-provoking work of economic storytelling, which links periodic religious awakenings to episodes of technological change and social reform movements. But the strain of Mr Fogel's work I have found most influential was that on the economic importance of the American railroad.

Prior to his contributions, the general view of the railroad was that its value to the American economy was immense, indeed revolutionary. Mr Fogel suggested that this shouldn't be taken for granted. Railway construction clearly lead to a redistribution of economic activity around the country, and toward the Midwest especially. But the cost savings of rail relative to alternatives, like canals, were not exceptionally large; a new transport technology didn't have to be hugely cheaper than alternatives to come to dominate the market. And just as markets optimised around railroad infrastructure after its construction (and later, around highways), they would have continued to optimise around canals and other transport modes in the absence of the railroad. Taking such things into consideration, he argued, rail still gave the American economy a boost, but of perhaps only a few percentage points of GDP.

Economists have continued to study the question, and some estimates now suggest that Mr Fogel's method, which calculated the "social savings" of the railroad, underestimated the contribution of the railroad. But the broader lesson—that one has to think critically about the counterfactual in trying to assess technologies or shocks or economic policy—has been an indispensible one for me.