Scope and methodology of international trade

The economic theory of international trade differs from the remainder of economic theory mainly because of the comparatively limited international mobility of the capital and labour. In that respect, it would appear to differ in degree rather than in principle from the trade between remote regions in one country. Thus the methodology of international trade economics differs little from that of the remainder of economics.

However, the direction of academic research on the subject has been influenced by the fact that governments have often sought to impose restrictions upon international trade, and the motive for the development of trade theory has often been a wish to determine the consequences of such restrictions.

The branch of trade theory which is conventionally categorized as "classical" consists mainly of the application of deductive logic, originating with Ricardo’s Theory of Comparative Advantage and developing into a range of theorems that depend on their practical value upon the realism of their postulates. "Modern" trade theory, on the other hand, depends mainly upon empirical analysis.

Classical theory

The law of comparative advantage provides a logical explanation of international trade as the rational consequence of the comparative advantages that arise from inter-regional differences - regardless of how those differences arise. Since its exposition by John Stuart Mill the techniques of neo-classical economics have been applied to it to model the patterns of trade that would result from various postulated sources of comparative advantage. However, extremely restrictive (and often unrealistic) assumptions have had to be adopted in order to make the problem amenable to theoretical analysis.

The best-known of the resulting models, the Heckscher-Ohlin theorem (H-O) depends upon the assumptions of no international differences of technology, productivity, or consumer preferences; no obstacles to pure competition or free trade and no scale economies. On those assumptions, it derives a model of the trade patterns that would arise solely from international differences in the relative abundance of labour and capital (referred to as factor endowments).

The resulting theorem states that, on those assumptions, a country with a relative abundance of capital would export capital-intensive products and import labour-intensive products. The theorem proved to be of very limited predictive value, as was demonstrated by what came to be known as the "Leontief Paradox" (the discovery that, despite its capital-rich factor endowment, America was exporting labour-intensive products and importing capital-intensive products). Nevertheless the theoretical techniques (and many of the assumptions) used in deriving the H-O model were subsequently used to derive further theorems.

The Stolper-Samuelson theorem, which is often described as a corollary of the H-O theorem, was an early example. In its most general form it states that if the price of a good rises (falls) then the price of the factor used intensively in that industry will also rise (fall) while the price of the other factor will fall (rise). In the international trade context for which it was devised it means that trade lowers the real wage of the scarce factor of production, and protection from trade raises it.

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THE EFFECTS OF TRADE: GAINS AND TERMS

There is a strong presumption that any exchange that is freely undertaken will benefit both parties, but that does not exclude the possibility that it may be harmful to others. However (on assumptions that included constant returns and competitive conditions) Paul Samuelson has proved that it will always be possible for the gainers from international trade to compensate the losers.

Moreover, in that proof, Samuelson did not take account of the gains to others resulting from wider consumer choice, from the international specialisation of productive activities - and consequent economies of scale, and from the transmission of the benefits of technological innovation. An OECD study has suggested that there are further dynamic gains resulting from better resource allocation, deepening specialisation, increasing returns to R&D, and technology spillover.

The authors found the evidence concerning growth rates to be mixed, but that there is strong evidence that a 1 per cent increase in openness to trade increases the level of GDP per capita by between 0.9 per cent and 2.0 per cent. They suggested that much of the gain arises from the growth of the most productive firms at the expense of the less productive. Those findings and others have contributed to a broad consensus among economists that trade confers very substantial net benefits, and that government restrictions upon trade are generally damaging.