Activities included in this sub-sector are the ones concerned with buying and selling products, either new or used goods, for distribution without changing the characteristics of the products.

According to the 1993 System of National Accounts traders are treated as supplying services rather than goods to their customers by storing and displaying a selection of goods in convenient locations and making them easily available for customers to buy. Their output is measured by the total value of the trade margins realised on the goods they purchase for resale. A trade margin is defined as the difference between the actual or imputed price realised on a good purchased for resale and the price that would have to be paid by the distributor to replace the good at the time it is sold or otherwise disposed of. The margins realised on some goods may be negative if their prices have to be marked down. They must be negative on goods that are never sold. The key is therefore to assess the trade margins on different kind of goods over time.

Table A2.1 gives aggregated trade margins from two trading houses in the period 1914-1939. Table A2.2 shows trade margins derived from the Input-Output tables.