Gross domestic product, GDP, is the total dollar value of all final goods and services produced in a country during a year. Several things about this definition should be noted:
1. Both goods, such as automobiles and top hats, and services, such as the help of lawyers and plumbers, are included.
2. Current market prices, reflecting the value society places on items, are used to aggregate different outputs to a dollar total. Government purchases, many of which do not occur on markets, are valued at their cost of production.
3. Only final goods and services are included. Intermediate goods, such as steel that has yet to be made into hammers and shovels, are not included. This practice avoids double-counting the steel.
4. This measure is an annual flow, a rate of production. A GDP of $6 trillion implies that the economy is producing $6 trillion worth of goods and services per year.
5. U.S. GDP measures production by U.S. citizens and foreigners alike inside the geographic borders of the United States and so unequivocally reflects economic activity in the United States.
Economists and the media use many names besides GDP to refer to the nation’s annual output of goods and services. Output, total output, national output, income, total income, national income, and aggregate supply are common. Algebraic representations use the capital letter Y. These names suggest that economists use the terminology output and income interchangeably; it is important to understand why.
The essence of why output and income are considered the same thing is that whatever is spent on a product (the value of that output) is divided up as income by those people producing it. Consider one element of GDP, a loaf of bread worth a dollar. With only a few exceptions, every penny of this dollar’s worth of bread can be traced back into somebody’s pocket as income. Some of the dollar is profit/proprietor income to the grocer, baker, miller, and farmer (or dividend income to their stockholders), some is wage and salary income to their employees, some is interest income to the banker who has financed their loans (or interest income to those who purchased their corporate bonds), and some is rental income to their landlords. It is because of this equivalence that total output, GDP, is referred to as total income.
Laypersons’ use of the word income is slightly different in that it reflects what we receive as income, regardless of whether or not it corresponds to output. There are three differences of note. First, of the dollar’s worth of bread, some money will be set aside by the grocer, baker, miller, and farmer to cover depreciation—to pay for replacing their buildings and equipment when they have worn out—and thus will never make it into anyone’s pocket as income. Second, if the grocer, baker, miller, or farmer pays any indirect taxes, such as sales taxes, as the bread makes its way through the production process, then this money goes directly to the government and thus also does not make it into anyone’s pocket as income. And third, transfer payments make up part of our income, but do not correspond to output produced. Examples are government production subsidies, welfare and unemployment insurance payments, and gifts. Interest on government and consumer debt is also classified as transfer payments because unlike interest paid by business, it does not reflect the cost of production activity. A subset of the national income accounts reports data on these kinds of measures.
As a nation, our annual income—what we have available to distribute to our citizens—is what we have produced during the year. Despite the fact that individual incomes do not quite match this concept of a nation’s aggregate income, we will use the terminologies aggregate output and aggregate income interchangeably. This thinking suggests that GDP could be measured by adding up all incomes and making adjustments for the phenomena that we have noted. For those interested, appendix 2.1 at the end of this chapter shows how this process would be carried out. Some countries use this method to help in estimating GDP, but the United States uses a different method.