It is early morning when a half-dozen senior officials enter the room at the Commerce Department in Washington. Once inside, they will have no communication with the outside world until they have completed their work later that day. They will have no telephone, no computer links. They will be able to slip out to an adjoining restroom, but only in pairs. It is no wonder the room is called “the Lockup.” The Lockup produces one of the most important indicators of economic activity we have: the official estimate of the value of the economy’s total output, known as its gross domestic product (GDP).

When the team has finished its computations, the results will be placed in a sealed envelope. A government messenger will hand carry the envelope to the Executive Office Building and deliver it to a senior adviser to the president of the United States. The adviser will examine its contents, then carry it across the street to the White House and give it to the president.

The senior officials who meet in secret to compute GDP are not spies; they are economists. The adviser who delivers the estimate to the president is the chairman of the Council of Economic Advisers.

The elaborate precautions for secrecy do not end there. At 7:30 the next morning, journalists from all over the world will gather in an electronically sealed auditorium at the Commerce Department. There they will be given the GDP figure and related economic indicators, along with an explanation. The reporters will have an hour to prepare their reports, but they will not be able to communicate with anyone else until an official throws the switch at 8:30. At that instant their computers will connect to their news services, and they will be able to file their reports. These will be major stories on the Internet and in the next editions of the nation’s newspapers; the estimate of the previous quarter’s GDP will be one of the lead items on television and radio news broadcasts that day.

The clandestine preparations for the release of quarterly GDP figures reflect the importance of this indicator. The estimate of GDP provides the best available reading of macroeconomic performance. It will affect government policy, and it will influence millions of decisions in the private sector. Prior knowledge of the GDP estimate could be used to anticipate the response in the stock and bond markets, so great care is taken that only a handful of trusted officials have access to the information until it is officially released.

The GDP estimate took on huge significance in the fall of 2008 as the United States and much of the rest of the world went through the wrenching experience of the worst financial crisis since the Great Depression of the 1930s. The expectation that the financial crisis would lead to an economic collapse was widespread, and the quarterly announcements of GDP figures were more anxiously awaited than ever.

The primary measure of the ups and downs of economic activity—the business cycle—is real GDP. When an economy’s output is rising, the economy creates more jobs, more income, and more opportunities for people. In the long run, an economy’s output and income, relative to its population, determine the material standard of living of its people.

Clearly GDP is an important indicator of macroeconomic performance. It is the topic we will consider in this chapter. We will learn that GDP can be measured either in terms of the total value of output produced or as the total value of income generated in producing that output. We will begin with an examination of measures of GDP in terms of output. Our initial focus will be on nominal GDP: the value of total output measured in current prices. We will turn to real GDP—a measure of output that has been adjusted for price level changes—later in the chapter. We will refer to nominal GDP simply as GDP. When we discuss the real value of the measure, we will call it real GDP.