Tariffs,the terms of trade,and national product differentiation

The assumption of national product differentiation is a common feature in many computable general equilibrium models currently used to evaluate trade policy. The results of these models tend to be dominated by changes in the terms of trade, rather than the efficiency effects of the policy concerned. In this paper we use a theoretical n-country general equilibrium trade model to evaluate how national product differentiation relates to the terms-of-trade effects of a tariff. We conclude that monopoly power implicit in national product differentiation is the source of the strong terms-of-trade effects in Armington-type models, and can be exercised with the imposition of a tariff. These results are independent of country size, thus yielding a nonzero optimal tariff even for a small country. Theoretical results are then illustrated using the importdisaggregated version of the Michigan model of world production and trade. We find that strong, tariff-induced terms-of-trade changes emerge over a wide range of import demand elasticities. These results suggest that the assumption of national product differentiation may prejudice the case in favor of maintaining existing levels of protection, and, therefore, may not be appropriate for commercial policy analysis.