Measures of national income & output

There are at least two or three different ways of calculating these numbers. The expenditure approach determines aggregate demand, or Gross National Expenditure, by summing consumption, investment, government expenditure and net exports. On the other hand, the income approach and the closely related output approach can be seen as the summation of consumption, savings and taxation. The three methods must yield the same results because the total expenditures on goods and services (GNE) must by definition be equal to the value of the goods and services produced (GNP) which must be equal to the total income paid to the factors that produced these goods and services (GNI). (GNP=GNI=GNE by definition)

In actual fact, there will be minor differences in the results obtained from the various methods due to changes in inventory levels. This is because goods in inventory have been produced (and therefore included in GDP), but not yet sold (and therefore not yet included in GNE). Similar timing issues can also cause a slight discrepancy between the value of goods produced (GDP) and the payments to the factors that produced the goods (particularly if inputs are purchased on credit).

Gross National Product

GDP counts income according to where it is earned rather than who owns the factors of production. In the above example, all of the income from the car factory would be counted as US GDP rather than German GDP.

To convert from GNP to GDP you must subtract factor income receipts from foreigners that correspond to goods and services produced abroad using factor inputs supplied by domestic sources. To convert from GDP to GNP you must add factor input payments to foreigners that correspond to goods and services produced in the domestic country using the factor inputs supplied by foreigners.

GDP is a better measure of the state of production in the short term. GNP is better when analysing sources and uses of income.

Depreciation and Net National Product

Not all of GNP is available to produce final goods and services - part of it represents output that is set aside to maintain the nation's productive capacity. Capital goods, such as buildings and machinery, lose value over time due to wear and tear and obsolescence. Depreciation measures the amount of GNP that must be spent on new capital goods to offset this effect.

In the Income Approach:

• Net National Product (NNP) is GNP minus depreciation
• Net National Income (NNI) is NNP minus indirect taxes
• Personal Income (PI) is NNI minus retained earnings, corporate taxes, transfer payments, and interest on the public debt
• Personal Disposable Income (PDI) is PI minus personal taxes, plus transfer payments.

Real and nominal values

Nominal GNP measures the value of output during a given year using the prices prevailing during that year. Over time, the general level of prices rise due to inflation, leading to an increase in nominal GNP even if the volume of goods and services produced is unchanged.

Real GNP measures the value of output in two or more different years by valuing the goods and services adjusted for inflation. For example, if both the "nominal GNP" and price level doubled between 1995 and 2005, the "real GNP" would remain the same. For year over year GNP growth, "real GNP" is usually used as it gives a more accurate view of the economy.

National income and welfare

GNP per person is often used as a measure of people's welfare. Countries with higher GNP often score highly on other measures of welfare, such as life expectancy. However, there are serious limitations to the usefulness of GNP as a measure of welfare:

• Measures of GNP typically exclude unpaid economic activity, most importantly domestic work such as childcare. This can lead to distortions; for example, a paid childminder's income will contribute to GNP, whereas an unpaid mother's time spent caring for her children will not, even though they are both carrying out the same economic activity.

• GNP takes no account of the inputs used to produce the output. For example, if everyone worked for twice the number of hours, then GNP might roughly double, but this does not necessarily mean that workers are better off as they would have less leisure time. Similarly, the impact of economic activity on the environment is not directly taken into account in calculating GNP.

• Comparison of GNP from one country to another may be distorted by movements in exchange rates. Measuring national income at purchasing power parity can help to overcome this problem.

• GNP does not take into account many factors that may be important to quality of life, such as the quality of the environment and security from crime. This can lead to distortions - for example, spending on cleaning oil spill is included in GDP, but the negative impact of the spill on well-being are not taken into account.

National accounting formulas (expenditure approach)

C = Personal consumption expenditures I = Gross private domestic investment G = Government consumption expenditures X = Net exports of goods and services M = Net imports of goods and services NR = Net income from assets abroad (net income receipts) CC = Consumption of fixed capital IBT = Indirect business taxes GDP = C + I + G + (X - M) GNP = C + I + G + (X - M) + NR NI = C + I + G + (X - M) + NR - CC - IBT

United States income and output