These are often used interchangeably though conceptually there is some difference among them. Difference between GNP and NNP arises because of depreciation (consumption of fixed capital).
There is same difference between GDP and NDP.
Difference between GNP and GDP arises because of Net Factor Income from Abroad (NFIA).
There is same difference between NNP and NDP.
All the above measures of national income can be calculated at market prices or factor costs. Difference between market prices and factor costs arises because of Net Indirect ‘Taxes (Indirect taxes Subsidies).
All the measures of national income discussed above can be calculated at either current prices or constant prices. When we use current prices (i.e., prices in the year for which national income is being calculated) to calculate value of goods and services, it is called national income at current prices or nominal national income.
On the contrary, when prices of a base year are taken to calculate national income then it is called national income at constant (or fixed prices) or real national income. At present, 1999-2000 is the base year for calculating NI at constant prices.
Conceptually real NNP at factor costs is the most accurate measure of national income but in India, real GDP at factor costs is mostly used because of some practical problems in measurement of depreciation and net factor income from abroad. Thus, economic growth in India generally refers to increase in real GDP at factor costs.
Some related concepts of national income are personal income and disposable personal income.
It is that income which is actually obtained by nationals of the economy. It is obtained by subtracting corporate taxes and payments for social securities provisions from national income and adding to it government transfer payments, business transfer payments and net interest paid by the government.
Disposable Personal Income:
When personal direct taxes are subtracted from personal income, the obtained value is called disposable personal income. In equation form:
Circular Flow of Income:
Basically there are three ways of looking at the circular flow of income. It arises out of the process of activity chain in which production creates income, income generates spending and spending in turn induces production.
Accordingly, there are three different ways in which we can measure the size of the circular flow. We can measure it either at the production stage by measuring the value of output, or at the income accrual stage by measuring the amount of factor income earned, or at the expenditure stage by measuring the size of total expenditure incurred in the economy.