He has undertaken work on David Ricardo's theory of comparative advantage, arguing that "the law of comparative advantage breaks down when applied to individual commodities or pairs of commodities in a many-commodity world", but stating that "that the law is nonetheless valid if restated in terms of averages across all commodities".
He has investigated David Ricardo's theory of comparative advantage, arguing that its application to individual goods or pairs is flawed in a multi-commodity world, but maintaining its validity when considered on an aggregate level across all commodities.