Spending in the economy takes many forms.
To understand how the economy is using its scarce resources, economists are often interested in studying the composition of GDP among various types of spending. To do this, GDP (denoted as Y) is divided into four components: Consumption (C), investment (I), Government purchases (G), and net exports (
NX);
Y = C + I + G + NXThe equation is an identity, - an equation that must be true by the way the variables in the equations are defined. In this case, because each dollar of expenditure included in GDP in placed into one of the four components of GDP, the total of the four components must be equal to GDP.
ConsumptionConsumption is spending by households on goods and services. "Goods" include household spending on durable goods, such as automobiles and appliances, and
non-durable goods, such as food and clothing. "Services" include each intangible items as haircuts and medical care. Household spending on
education is also included in consumption of services (although one might argue that it would fit better in the next component).
InvestmentInvestment is the purchase of goods that will be used in the future to produce more goods and services. It is the sum of purchases of caputal equipkent, inventories, and structures. Investment in structures includes expenditure on new housing. By convention, the puchase of a new house is the one form of household spending categorized as investment rather than consumption.
The treatment of inventory accumulation is noteworthy. When IBM produces a computer and, instead of selling, IBM adds it to the inventory, IBM is assumed to have "purchased" the computer for itself. That is, the national income accountants treat the computer as part of IBM's investment spending. Inventories are treated in this way because one aim of GDP is to measure the value of economy's production, and goods added to inventory are part of that period's production.
Government PurchasesGovernment purchases include spending on goods and services by local, state and federal governments. It includes the salaries of government workers and spending on public works.
The meaning of "Government Purchases" requires a bit of clarification. When the government pays the salary of an Army general, that salary is part of Government purchases. But what happens when the government pays a Social Security benefit to one of the elderly? Such government spending is called a transfer payment because it is not made in exchange ofr a currently produced good or service.
Transfer payments alter household income, but they do not reflect the economy;s production. (From a macroeconomic standpoint, transfer payments are like negative taxes.) Because GDP is intended to measure income from, and expenditure on, the production of goods and services, transfer payments are not counted as part of government purchases.
Net ExportsNet Exports equal the pucahses of domestically produces goods by foreigners (exports) minus the domestic purchases of foreign goods (imports). A domestic firm's sale to a buyer in an another country, such as Boeing sale to British Airways, increases net exports.