Kravis:

Availability" theory: Kravis (1956) states that a country tends to import products that are not available at home; 'availability' is determined by natural resources, technological progress and product differentiation. The availability theory is a theory of the determinants of international trade, due to Kravis (1956) that says that countries import what they do not have available domestically and export what they do. The theory can be said to encompass explanations of trade that stress factor endowments, technological differences, and product differentiation. Irving B. Kravis made a number of remarkable contributions to the study of comparative economic structure, especially of quantities and prices. Kravis's research has served as a model for students and colleagues alike in the testing of theory against facts. Kravis made important contributions in several areas of international economics, often with new insights for public policy. These include critiques of import and export price indexes, an evaluation of the role of trade in economic growth, studies of the world income distribution, productivity comparisons, analyses of the determinants of national price levels, and the role of multinationals in world trade.

His most path-breaking work was in developing real product comparisons and estimating purchasing-power parities for countries around the world. This was done first for Western Europe in the early 1950's and then again on a grand scale when he directed the United Nations International Comparison Project from 1968 to 1982. In the latter effort, multilateral techniques were worked out, inevitably representing a compromise between practical and theoretical considerations that made it possible to compare real quantities and price parities in different countries at various levels of aggregation. This represented the first giant steps toward realizing a full worldwide national accounts system that permits real interspatial as well as intertemporal quantity comparisons. The output from this is widely used today and the analysis has become a routine exercise of the European Community and the OECD countries. Altogether, by now more than 80 countries have participated in this work, essentially following the methods established under Kravis's leadership.