Measures of national income and output are used in economics to estimate the welfare of an economy through totaling the value of goods and services produced in an economy. They use a system of national accounting first developed during the 1940s. The primary measures of national income and output are Gross Domestic Product (GDP), Gross National Product (GNP), Gross National Income (GNI), Net National Product (NNP), and Net National Income (NNI).
There are three main ways of calculating these numbers; the output approach, the income approach and the expenditure approach. In theory, the three must yield the same, because total expenditures on goods and services (GNE) must equal the total income paid to the producers (GNI), and that must also equal the total value of the output of goods and services (GNP).
However, in practice minor differences are obtained from the various methods due to changes in inventory levels. This is because goods in inventory have been produced (therefore included in GNP), but not yet sold (therefore not yet included in GNE). Similar timing issues can also cause a slight discrepancy between the value of goods produced (GNP) and the payments to the factors that produced the goods, particularly if inputs are purchased on credit, and also because wages are collected often after a period of production.
To give an example of the difference between GDP and GNP, and also income, using United States:
|Gross national product||11,059.3|
|Net U.S. income receipts from rest of the world||55.2|
|U.S. income receipts||329.1|
|U.S. income payments||273.9|
|Gross domestic product||11,004.1|
|Private consumption of fixed capital||1,135.9|
|Government consumption of fixed capital||218.1|
GNP is becoming less used, as a larger number of nationals are working in nations abroad. Because of this, GDP is becoming a more popular measure.
A number of ratios are derived from GDP. These include:
These terms often use "expenditure", or "income" instead of "product". These are still the same, as for all goods that are produced, an amount of money equal to the value of the goods produced is spent on purchasing the goods, and the money spent purchasing the goods is paid to the workers as income. Therefore, production, expenditures, and income are all equal.
Also, "domestic" is often substituted with "national", as explained in GDP vs. GNP.
Because of the complication of the multiple stages in the production of a good or service, only the final value of a good or service is included. This avoids an issue often referred to as "double counting" - when the total value of a good is included in the national output in several stages of production. In the example of meat production, the value of the good from the farm may be $10, then $30 from the butchers, and then $60 from the supermarket. The value that should be included in final national output should be $60, not the sum of all those numbers, $100. The values added at each stage of production over the previous stage are respectively $10, $20, and $30. Their sum gives an alternative way of calculating the value of final output.
The method of National Income by Output, Value Added method:
GDP at market price = Value of Output in an economy in a particular year - Intermediate consumption
NNP at factor cost = GDP at market price - Depreciation + NFIA (Net Factor Income from Abroad) - Net Indirect Taxes
The main types of income that are included in this measurement are rent (the money paid to owners of land), salaries and wages (the money paid to workers who are involved in the production process, and those who provide the natural resources), interest (the money paid for the use of man-made resources, such as machines used in production), and profit (the money gained by the entrepreneur - the businessman who combines these resources to produce a good or service).
The equation for measurement of National Income by Income Method:
NDP at factor cost = compensation of employee + operating surplus + Mixed income of self employee
National Income = NDP at factor cost + NFIA (net factor income from abroad)
C = Household consumption expendituresPersonal consumption expenditures
I = Gross private domestic investment
G = Government consumption and gross investment expenditures
X = Gross exports of goods and services
M = Gross imports of goods and services
Note: (X - M) is often written as NX, which stands for "Net Exports"
Because of this, other measures of welfare such as the Human Development Index (HDI), Index of Sustainable Economic Welfare (ISEW), Genuine Progress Indicator (GPI), Gross National Happiness (GNH) and Sustainable National Income (SNI) are used.