Measuring the Size of the Economy: Gross Domestic Product

Macroeconomics is an empirical subject, meaning that it is verifiable by observation or experience rather than theory. Given this, the first step toward understanding macroeconomic concepts is to measure the economy.

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How large is the U.S. economy? The size of a nation’s overall economy is typically measured by its gross domestic product (GDP), which is the value of all final goods and services produced within a country in a given year. The measurement of GDP involves counting up the production of millions of different goods and services—smart phones, cars, music downloads, computers, steel, bananas, college educations, and all other new goods and services produced in the current year—and summing them into a total dollar value. This task is straightforward: take the quantity of everything produced, multiply it by the price at which each product sold, and add up the total. In 2014, the U.S. GDP totaled $17.4 trillion, the largest GDP in the world.

Each of the market transactions that enter into GDP must involve both a buyer and a seller. The GDP of an economy can be measured either by the total dollar value of what is purchased in the economy, or by the total dollar value of what is produced. There is even a third way, as we will explain later.

GDP Measured by Components of Demand

Who buys all of this production? This demand can be divided into four main parts:

consumer spending (consumption)business spending (investment)government spending on goods and servicesspending on net exports

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What is meant by the word “investment”?

What do economists mean by investment, or business spending? In calculating GDP, investment does not refer to the purchase of stocks and bonds or the trading of financial assets. It refers to the purchase of new capital goods, that is, new commercial real estate (such as buildings, factories, and stores) and equipment, residential housing construction, and inventories. Inventories that are produced this year are included in this year’s GDP—even if they have not yet sold. From the accountant’s perspective, it is as if the firm invested in its own inventories. Business investment in 2012 was over $2 trillion, according to the Bureau of Economic Analysis.

Table 5.1 shows how these four components added up to the GDP in 2012. Figure 5.4 (a) shows the levels of consumption, investment, and government purchases over time, expressed as a percentage of GDP, while Figure 5.4 (b) shows the levels of exports and imports as a percentage of GDP over time. A few patterns about each of these components are worth noticing. Table 5.1 shows the components of GDP from the demand side. Figure 5.3 provides a visual of the percentages.


 Table 5.1. Components of U.S. GDP in 2012: From the Demand Side
Components of GDP on the Demand Side (in trillions of dollars)Percentage of Total
 Consumption $11.1 68.6%
 Investment $2.5 15.2%
 Government $3.2 19.5%
 Exports $2.2 13.5%
 Imports –$2.7 –16.9%
 Total GDP $16.2 100%
Source: http://bea.gov/iTable/iTable.cfm?ReqID=9&step=1

Percentage of Components of U.S. GDP on the Demand Side


Figure 5.3. Percentage of Components of U.S. GDP on the Demand Side. Consumption makes up over half of the demand side components of the GDP. (Source: http://bea.gov/iTable/iTable.cfm?ReqID=9&step=1).


Components of GDP on the Demand Side


Figure 5.4. Components of GDP on the Demand Side (a) Consumption is about two-thirds of GDP, but it moves relatively little over time. Business investment hovers around 15% of GDP, but it increases and declines more than consumption. Government spending on goods and services is around 20% of GDP. (b) Exports are added to total demand for goods and services, while imports are subtracted from total demand. If exports exceed imports, as in most of the 1960s and 1970s in the U.S. economy, a trade surplus exists. If imports exceed exports, as in recent years, then a trade deficit exists. (Source: http://bea.gov/iTable/iTable.cfm?ReqID=9&step=1).


Consumption expenditure by households is the largest component of GDP, accounting for about two-thirds of the GDP in any year. This tells us that consumers’ spending decisions are a major driver of the economy. However, consumer spending is a gentle elephant: when viewed over time, it does not jump around too much.

Investment expenditure refers to purchases of physical plant and equipment, primarily by businesses. If Starbucks builds a new store, or Amazon buys robots, these expenditures are counted under business investment. Investment demand is far smaller than consumption demand, typically accounting for only about 15–18% of GDP, but it is very important for the economy because this is where jobs are created. However, it fluctuates more noticeably than consumption. Business investment is volatile; new technology or a new product can spur business investment, but then confidence can drop and business investment can pull back sharply.

If you have noticed any of the infrastructure projects (new bridges, highways, airports) launched during the recession of 2009, you have seen how important government spending can be for the economy. Government expenditure in the United States is about 20% of GDP, and includes spending by all three levels of government: federal, state, and local. The only part of government spending counted in demand is government purchases of goods or services produced in the economy. Examples include the government buying a new fighter jet for the Air Force (federal government spending), building a new highway (state government spending), or a new school (local government spending). A significant portion of government budgets are transfer payments, like unemployment benefits, veteran’s benefits, and Social Security payments to retirees. These payments are excluded from GDP because the government does not receive a new good or service in return or exchange. Instead they are transfers of income from taxpayers to others.

HOW DO STATISTICIANS MEASURE GDP?

Government economists at the Bureau of Economic Analysis (BEA), within the U.S. Department of Commerce, piece together estimates of GDP from a variety of sources.

Once every five years, in the second and seventh year of each decade, the Bureau of the Census carries out a detailed census of businesses throughout the United States. In between, the Census Bureau carries out a monthly survey of retail sales. These figures are adjusted with foreign trade data to account for exports that are produced in the United States and sold abroad and for imports that are produced abroad and sold here. Once every ten years, the Census Bureau conducts a comprehensive survey of housing and residential finance. Together, these sources provide the main basis for figuring out what is produced for consumers.

For investment, the Census Bureau carries out a monthly survey of construction and an annual survey of expenditures on physical capital equipment.

For what is purchased by the federal government, the statisticians rely on the U.S. Department of the Treasury. An annual Census of Governments gathers information on state and local governments. Because a lot of government spending at all levels involves hiring people to provide services, a large portion of government spending is also tracked through payroll records collected by state governments and by the Social Security Administration.

With regard to foreign trade, the Census Bureau compiles a monthly record of all import and export documents. Additional surveys cover transportation and travel, and adjustment is made for financial services that are produced in the United States for foreign customers.

Many other sources contribute to the estimates of GDP. Information on energy comes from the U.S. Department of Transportation and Department of Energy. Information on healthcare is collected by the Agency for Health Care Research and Quality. Surveys of landlords find out about rental income. The Department of Agriculture collects statistics on farming.

All of these bits and pieces of information arrive in different forms, at different time intervals. The BEA melds them together to produce estimates of GDP on a quarterly basis (every three months). These numbers are then “annualized” by multiplying by four. As more information comes in, these estimates are updated and revised. The “advance” estimate of GDP for a certain quarter is released one month after a quarter. The “preliminary” estimate comes out one month after that. The “final” estimate is published one month later, but it is not actually final. In July, roughly updated estimates for the previous calendar year are released. Then, once every five years, after the results of the latest detailed five-year business census have been processed, the BEA revises all of the past estimates of GDP according to the newest methods and data, going all the way back to 1929.


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Trade Balance

When thinking about the demand for domestically produced goods in a global economy, it is important to count spending on exports—domestically produced goods that are sold abroad. By the same token, we must also subtract spending on imports—goods produced in other countries that are purchased by residents of this country. The net export component of GDP is equal to the dollar value of exports (X) minus the dollar value of imports (M), (X – M). The gap between exports and imports is called the trade balance. If a country’s exports are larger than its imports, then a country is said to have a trade surplus. In the United States, exports typically exceeded imports in the 1960s and 1970s, as shown in Figure 5.4 (b).

Since the early 1980s, imports have typically exceeded exports, and so the United States has experienced a trade deficit in most years. Indeed, the trade deficit grew quite large in the late 1990s and in the mid-2000s. Figure 5.4 (b) also shows that imports and exports have both risen substantially in recent decades, even after the declines during the Great Recession between 2008 and 2009. As noted before, if exports and imports are equal, foreign trade has no effect on total GDP. However, even if exports and imports are balanced overall, foreign trade might still have powerful effects on particular industries and workers by causing nations to shift workers and physical capital investment toward one industry rather than another.

Based on these four components of demand, GDP can be measured as:

GDP = Consumption + Investment + Government + Trade balance

GDP = C + I + G + (X – M)

Understanding how to measure GDP is important for analyzing connections in the macro economy and for thinking about macroeconomic policy tools.

GDP Measured by What is Produced

Everything that is purchased must be produced first. Table 5.2 breaks down what is produced into five categories: durable goods,nondurable goods, services, structures, and the change in inventories. Before going into detail about these categories, notice that total GDP measured according to what is produced is exactly the same as the GDP measured by looking at the five components of demand. Figure provides a visual representation of this information.

 Table 5.2. Components of GDP on the Supply Side
Components of GDP on the Supply Side (in trillions of dollars)Percentage of Total
 Goods
Durable goods $2.7 16.6%
Nondurable goods $4.7 29.1%
 Services $7.6 46.7%
 Structures$1.2 7.2%
Changes in inventories$0.1 0.4%
 Total GDP $16.3 100%
Source: http://bea.gov/iTable/iTable.cfm?ReqID=9&step=1

Percentage of Components of GDP on the Production Side


Figure 3. Services make up almost half of the production side components of GDP in the United States. (Source: http://bea.gov/iTable/iTable.cfm?ReqID=9&step=1).


Since every market transaction must have both a buyer and a seller, GDP must be the same whether measured by what is demanded or by what is produced. Figure 4 shows these components of what is produced, expressed as a percentage of GDP, since 1960.

Types of Production


Figure 4. Services are the largest single component of total supply, representing over half of GDP. Nondurable goods used to be larger than durable goods, but in recent years, nondurable goods have been dropping closer to durable goods, which is about 20% of GDP. Structures hover around 10% of GDP. The change in inventories, the final component of aggregate supply, is not shown here; it is typically less than 1% of GDP.


In thinking about what is produced in the economy, many non-economists immediately focus on solid, long-lasting goods, like cars and computers. By far the largest part of GDP, however, is services. Moreover, services have been a growing share of GDP over time. A detailed breakdown of the leading service industries would include healthcare, education, and legal and financial services. It has been decades since most of the U.S. economy involved making solid objects. Instead, the most common jobs in a modern economy involve a worker looking at pieces of paper or a computer screen; meeting with co-workers, customers, or suppliers; or making phone calls.

Even within the overall category of goods, long-lasting durable goods like cars and refrigerators are about the same share of the economy as short-lived nondurable goods like food and clothing. The category of structures includes everything from homes, to office buildings, shopping malls, and factories. Inventories is a small category that refers to the goods that have been produced by one business but have not yet been sold to consumers, and are still sitting in warehouses and on shelves. The amount of inventories sitting on shelves tends to decline if business is better than expected, or to rise if business is worse than expected.

The Problem of Double Counting

GDP is defined as the current value of all final goods and services produced in a nation in a year. What are final goods? They are goods at the furthest stage of production at the end of a year. Statisticians who calculate GDP must avoid the mistake of double counting, in which output is counted more than once as it travels through the stages of production. For example, imagine what would happen if government statisticians first counted the value of tires produced by a tire manufacturer, and then counted the value of a new truck sold by an automaker that contains those tires. In this example, the value of the tires would have been counted twice-because the price of the truck includes the value of the tires.

To avoid this problem, which would overstate the size of the economy considerably, government statisticians count just the value of final goods and services in the chain of production that are sold for consumption, investment, government, and trade purposes.Intermediate goods, which are goods that go into the production of other goods, are excluded from GDP calculations. From the example above, only the value of the Ford truck will be counted. The value of what businesses provide to other businesses is captured in the final products at the end of the production chain.

The concept of GDP is fairly straightforward: it is just the dollar value of all final goods and services produced in the economy in a year. In our decentralized, market-oriented economy, actually calculating the more than $16 trillion-dollar U.S. GDP—along with how it is changing every few months—is a full-time job for a brigade of government statisticians.

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Counting GDP

What is counted in GDP?

ConsumptionBusiness investmentGovernment spending on goods and servicesNet exports

What is not included in GDP?

Intermediate goodsTransfer payment and non-market activitiesUsed goodsIllegal goods

Notice the items that are not counted into GDP, as outlined in the list above. The sales of used goods are not included because they were produced in a previous year and are part of that year’s GDP. The entire underground economy of services paid “under the table” and illegal sales should be counted, but is not, because it is impossible to track these sales. In a recent study by Friedrich Schneider of shadow economies, the underground economy in the United States was estimated to be 6.6% of GDP, or close to $2 trillion dollars in 2013 alone. Transfer payments, such as payment by the government to individuals, are not included, because they do not represent production. Also, production of some goods—such as home production as when you make your breakfast—is not counted because these goods are not sold in the marketplace.