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Article

Scott Baier and Samuel Standaert

The gravity model of international trade states that the volume of trade between two countries is proportional to their economic mass and a measure of their relative trade frictions. Perhaps because of its intuitive appeal, the gravity model has been the workhorse model of international trade for more than 50 years. While the initial empirical work using the gravity model lacked sound theoretical underpinnings, the theoretical developments have highlighted how a gravity-like specification can be derived from many models with varying assumptions about preferences, technology, and market structure. Along the strengthening of the theoretical roots of the gravity model, the way in which it is estimated has also evolved significantly since the start of the new millennium. Depending on the exact characteristics of regression, different estimation methods should be used to estimate the gravity model.

Article

Models of comparative advantage in international trade explain specialization using differences in autarky relative prices. This literature has traditionally focused on the Heckscher–Ohlin and Ricardian models. The former emphasizes differences in factor abundance across countries and in factor intensity across goods; the latter focuses on relative productivity differences across countries and goods. However, unrealistic assumptions and stark assumptions have hindered empirical assessment of these models. Contemporary models now allow researchers to overcome these hurdles. New models of Ricardian comparative advantage incorporate realistic geography and multiple countries. Similar advances have freed the Heckscher–Ohlin model from some of its theoretical straightjackets. In addition, researchers have started to provide microfoundations for the Ricardian model and to formalize how institutions and factor market distortions might generate patterns of comparative advantage. Trade economists have also started to think about magnitudes in a different way; that is, through general equilibrium counterfactual experiments.

Article

Pao-Li Chang and Wen-Tai Hsu

This article reviews interrelated power-law phenomena in geography and trade. Given the empirical evidence on the gravity equation in trade flows across countries and regions, its theoretical underpinnings are reviewed. The gravity equation amounts to saying that trade flows follow a power law in distance (or geographic barriers). It is concluded that in the environment with firm heterogeneity, the power law in firm size is the key condition for the gravity equation to arise. A distribution is said to follow a power law if its tail probability follows a power function in the distribution’s right tail. The second part of this article reviews the literature that provides the microfoundation for the power law in firm size and reviews how this power law (in firm size) may be related to the power laws in other distributions (in incomes, firm productivity and city size).

Article

While the modern theory of international trade allows for many different modeling assumptions, the gains from trade can often be calculated using a common set of statistics. In particular, the share of a country’s output that is consumed domestically, the elasticity of bilateral trade with respect to trade costs, and the relationship between markups and firm size, each have a clear role in the gains from integration. All of these statistics may also be structurally linked to the degree of firm heterogeneity, usually the dispersion in firm-level productivity. Accordingly, the presence of firm heterogeneity may have a meaningful impact on the welfare response to trade liberalization. A quantitative application of a common firm heterogeneity model indicates that increased dispersion of firm-level productivity has a disproportionately large and positive impact on the gains from trade for smaller, less-developed countries.