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This article describes the difficulty of moving from exporting one product to exporting another in terms of a “distance” between various products. I would imagine, however, that a nation that already manufactures computers, for example, could easily move into calculators, but that the reverse might not be true. Did the researchers consider the directionality of their links?

Jesse Ziser
Austin, Texas

Cesar Hidalgo of the University of Notre Dame in Indiana says that although the model described in the story didn’t have directional links, he and his colleagues are working on a version that would include this possibility. —D. Castelvecchi