National income can be considered in three ways, as Fig. 133 (a) suggests:
All three measures outlined above show the gross money value of goods and services produced - the gross national product. In the process of producing these goods and services, however, the nation's capital stock will be subject to wear and tear, so we must allow for the net money value of goods and services produced (allowing for the depreciation of the capital stock or CAPITAL CONSUMPTION) - the NET NATIONAL PRODUCT. This net national product is called national income.
In practice, data-collection problems mean that the three measures of national income give slightly different figures, necessitating the introduction of a residual error term in the national income accounts that reflects these differences. Additionally, in order to highlight the difference in the money and REAL VALUE of national income, it is necessary to take account of the effects of INFLATION upon GNP by applying a broad-based PRICE INDEX, called the GNP-DEFLATOR. See alsoBLACK ECONOMY.
By way of a ‘practical’ example, Fig. 133 gives a ‘standard’ expenditure-based breakdown of the UK's gross domestic product (GDP), which is used by the government for economic policy purposes.