10.35 Of all the flows in the economy, the changes in the value of the flows of goods and market services are the most readily broken down into price and volume changes. In this context a clear distinction should be made between:
10.37 The flows in category b), which are notional transactions, are typified by the absence of an actual price for the transaction. This is the case for such goods as agricultural products for own final use and goods for fixed capital formation on own-account. For services, the most important type refers to owner-occupied dwellings. Values for these imputed flows are to be obtained by applying prices of similar products when marketed and the deflator should therefore be the same. Since it is usually necessary to value output of own-account construction by costs of production rather than prices, the deflator has to be adjusted in this respect.
10.38 The most important flows in category c) are those whose value at current prices is obtained as a difference between the values of two flows of goods. This arises in the case of trade margins, whose value at current prices is defined as the difference between the actual or imputed price realised on a good purchased for resale by the wholesale and retail trades and the price that would have to be paid by the distributor to replace the good at the time it was sold or otherwise disposed of. By one method, estimates of trade margins at constant prices can therefore also be made by difference, by subtracting the constant-price value of goods bought for resale from the constant-price value of goods resold by these trades. An alternative method of measurement would be to extrapolate the trade margins of the base year either by the volume of sales or by the volume of purchases made by the wholesale and retail trades. To be correct, this alternative has to take into account the fact that trade margins vary amongst different products and uses. This is explicitly acknowledged in the supply and use tables.
10.39 Category c) also includes output of travel agency services measured as the value of service charges of agencies and (fees and commission charges). These services can also be measured as the difference between two flows the full payment made by the purchaser and the expenditure made for transport and accommodation by the producer. The volume measure can be obtained as the difference between these flows calculated at constant prices. Alternatively, the fee or commission can be defined as the price per unit of the type of transportation or accommodation arranged and the volume indicator for the service charge would therefore move in the same way as these flows.
10.40 The flows in category d) consist of financial intermediation services, service charges from insurance and pension funds are also included. Financial intermediation services are provided by banks and other financial corporations and consist of lending money to businesses or households, providing a safe and convenient means of saving, safeguarding money and other valuables, buying and selling foreign currencies, clearing cheques, providing general economic intelligence, dealing in stocks and bonds, and offering investment advice. In some cases these services are easily defined and specifically paid for, e.g. in the case of renting space in bank vaults, or when fees are charged in connection with issues of stocks, bonds or loans. The current value of transactions can then be defined, as well as prices and quantities necessary for price and volume measurement. However, a breakdown into price and volume components for financial intermediation services indirectly measured and for insurance services can usually only be made on arbitrary grounds and would have to be based on conventions.