Methods of Measuring National Income

National income can be measured in three internationally accepted ways. Each looks at the same circular flow of income from a different point — production, income, or spending — and in principle all three give the same total. A country's statistical agency uses whichever method has the most reliable data for a given sector.

1. Product (or Value Added) Method — sums the value added by every producing enterprise, industry by industry (agriculture, mining, manufacturing, trade, transport, services, and so on), after removing the value of intermediate inputs so that nothing is counted twice:

Value added = value of output − value of intermediate consumption. This method works best where physical output data is reliable, such as agriculture and organised manufacturing.

2. Income Method — sums the incomes earned by the owners of the factors of production employed in producing that output:

Adding net factor income from abroad converts this domestic total (NDP at factor cost) into National Income (NNP at factor cost). This method suits the organised sector, where wage and profit records exist.

3. Expenditure Method — sums all final expenditure on domestically produced goods and services:

where $C$ is private final consumption expenditure, $I$ is gross domestic capital formation (investment), $G$ is government final consumption expenditure, and $(X - M)$ is net exports (exports minus imports). This is the method relied on most for the services (tertiary) sector, where direct output data is hard to record but spending flows can be tracked through surveys. …