TERMS OF TRADE
The relation between the prices of a country's exports and the prices of its imports, represented arithmetically by taking the export index as a percentage of the import index. In the comparative cost model, terms of trade were, defined as the international exchange ratio between a country's export good and its import good. This is the barter terms of trade which measures the quantity of exports which have to be sacrificed to obtain a unit of imports and is easily calculated when there are just two goods traded. But in practice, countries trade hundreds of different goods and services and the concept of the terms of trade becomes more complex. Estimates of the terms of trade are usually made by calculating an index of import prices; this gives an index of the term of trade:
Terms of trade index = Export Price Index x 100
Import Price Index
Thus, the price indices are essentially weighted averages of export and import pries. If these are set at 100 in the same base year, say, 1990, then the terms of trade index is also 100. If, for instance, import prices fall relative to export prices, the terms of trade will rise above 100, the terms of trade then being said to be more favourable to the country concerned since it means that it can obtain more goods from abroad than before in exchange for a given quantity of exports. On the other hand, if the terms of trade become unfavourable, the terms of trade index will fall below 100.
A rise in terms of trade index is usually described as an "improvement" or as "favourable" on the grounds that a rise in export prices relative to import prices theoretically means that a country can now buy the same quantity of imports for the sacrifice of less export (or it can have more imports for the same volume of exports). Similarly, a fall in the terms of trade index is a "deterioration" or is an "unfavourable" movement.