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the back story on front page economics

November ■ 2012

The Output Gap: A “Potentially”
Unreliable Measure of Economic Health?
Elise A. Marifian, Research Analyst
“‘Is real output greater or less than potential?’ and ‘Is real output growing more or less rapidly than potential?’
The answers to these questions are central to policy decisions.”
—Richard G. Anderson, Vice President and Economist, Federal Reserve Bank of St. Louis, 2009

The Great Recession ended almost three years ago, but in many ways it seems like the
economy is still in a rut. Amid financial instability in Europe and uncertainty about the future
of the U.S. business climate, many firms seem reluctant to expand and invest. The numbers of
mortgage delinquencies and foreclosures remain high despite recent improvements in housing
starts and prices. And while monthly consumer spending indicators are improving steadily,
many American families continue to struggle with the challenges of unemployment and underemployment. Given these realities, some economists and policymakers believe that the economy
has not yet returned to a “normal” functioning level.
But what exactly is the economy’s “normal” functioning level? How many people could be
working and how much could they be producing?1 Economists use the notion of potential
output (potential real gross domestic product [GDP]) to represent a normal—or benchmark—
level of output against which actual output (real GDP) can be compared at any given time.
Potential output is the amount the economy would produce given the quantity and quality of
the nation’s factors of production: capital (equipment and structures), technology, and worker
knowledge. The economy’s “normal” functioning is characterized by this level of potential output and the corresponding level of employment. Depending on the state of the economy, actual
output could be above, below, or equal2 to potential output (see the chart, which plots U.S.
potential output and actual output over the past 50 years). The difference between potential
output and actual output—or, in other words, the difference between where the economy would
be normally and where it is now—is known as the output gap.3 The output gap is one of many
economic measures that policymakers use to evaluate our economic performance.
Actual output, or real GDP, is a straightforward calculation because what the economy has
produced is quantifiable. Calculating potential GDP, however, is not so straightforward; it is a
modeling exercise, albeit one that uses actual data as inputs. In other words, potential GDP is
a hypothetical number. For that reason, economists and policymakers must exercise caution
when interpreting movements in the output gap—especially when potential GDP is estimated
from the most recently available data.
Some economists question the reliability of potential output (and, therefore, output gap)
measures. For instance, as James Bullard4 noted in 2009, if calculations had considered the
housing boom and bust, then potential GDP and output gap measurements would have been



Federal Reserve Bank of St. Louis

U.S. Real GDP Versus Potential Real GDP

Trillions of
U.S. Dollars




Output Gap



Potential Real GDP
Real GDP



NOTE: The figure plots potential and actual GDP, showing the fluctuations of the U.S. output gap over the past 50 years.
When potential output exceeds actual output, the output gap is negative, the economy is considered to be underperforming, and the unemployment rate is rising. Alternatively, when actual output exceeds potential output, the output gap is
positive, and the economy is considered to be overheating and at risk of inflation. When the two measures are equal,
prices are stable and the economy is at full employment. The CBO (2011, p. 43) defines “full employment” as “the level of
employment consistent with CBO’s estimate of the natural rate of unemployment and its projection of the potential labor
force.” For information on the natural rate of unemployment, see Armenter (2011).
SOURCE: Real GDP and Real Potential GDP (Quarterly Series, 2005 Chained), Federal Reserve Economic Data (FRED),
Federal Reserve Bank of St. Louis.

smaller than they appeared.5 His view suggests a problem with the inherent theoretical framework many economists use to measure output gaps. Another problem is that the estimates of
potential and actual GDP are revised because (i) the underlying data are updated as more information becomes available and (ii) new methodologies are adopted to estimate potential output.
Given these concerns, how can economists accurately estimate what the economy should
produce now and in the future? Herein lies the questionable nature of using measurements of
the output gap in policy decisions: As more time allows for more accurate calculations, the
estimates are revised—sometimes significantly. If initial estimates misrepresent the state of the
economy, then important monetary and fiscal policy decisions based on these estimates could
prove misguided.
For instance, economist Athanasios Orphanides (2002, 2003) suggests that using initial output gap estimates contributed importantly to the increased inflation of the 1970s.6 He argues
that the Federal Reserve, believing the output gap to be more negative than it really was, took
overly stimulative actions that produced an overheated and inflation-ridden economy.7
What about the output gap today? Similar to Orphanides’ findings, Gavin (2012) shows
that the output gap calculations for 2003-12 are reduced significantly when 2011 estimates of
potential GDP are used in place of 2007 estimates.8 If our economy is improving faster than
current output gap measurements suggest, then monetary policy intended to boost the economy
could produce too much stimulation, thereby fueling inflation once the economy begins to pick
up steam. ■




Federal Reserve Bank of St. Louis



Our country’s long-term growth is largely a function of the factors that influence how productive we are as a society.

2 When

real GDP is at potential (the output gap is zero), the unemployment rate equals its natural rate and prices are stable
(see Kliesen, 1999, and Armenter, 2011). More information on unemployment can be found at the Federal Reserve Bank of
St. Louis Economic Resources website (“Unemployment—The Economic Lowdown Podcast Series”).
3 The concepts of potential output and the output gap described in this essay fall largely within a New Keynesian macroeconomic framework, which many economists and Federal Open Market Committee policymakers use to analyze the economy
and determine the appropriate stance of monetary policy. Others in the economics profession would describe potential output and the output gap in a different way. More information on different economic schools of thought can be found in the
November 2009 Liber8 Economic Information Newsletter.

James Bullard is the president and CEO of the Federal Reserve Bank of St. Louis.


For further discussion of how the real estate bubble biased the output gap, see Banternghansa and Peralta-Alva (2009).

6 For more information on the Great Inflation of the 1970s and early 1980s, see the October 2012 Page One Economics Newsletter.

See Lubik and Slivinski (2010).


Gavin shows that Congressional Budget Office (CBO) estimates of the output gap based on 2007-vintage potential GDP are
much larger than estimates using 2011-vintage potential GDP. For instance, based on 2007-vintage data, the output gap for
the first quarter of 2009 was –9.9 percent, compared with –7.1 percent, which results when 2011-vintage data (based on
revised data) for potential GDP are used.

Anderson, Richard G. “Editor’s Introduction.” Federal Reserve Bank of St. Louis Review, July/August 2009, 91(4), pp. 181-85.
Armenter, Roc. “Output Gaps: Uses and Limitations.” Federal Reserve Bank of Philadelphia Business Review, Quarter 1, 2011,
pp. 1-8.
Banternghansa, Chanont and Peralta-Alva, Adrian. “Has the Recent Real Estate Bubble Biased the Output Gap?” Federal
Reserve Bank of St. Louis Monetary Trends, 2009, No. 45, December 16, 2009.
Bullard, James. “Three Issues for Near-Term Monetary Policy.” Presented at the National Association of Business Economics
51st Annual Conference, “The New Global Financial and Economic Architecture: Gateway to Recovery (or Just More of the
Blues?),” October 11-13, 2009, St. Louis, Missouri.
Congressional Budget Office. Budget and Economic Outlook: Fiscal Years 2011 to 2021. January 26, 2011.
Gavin, William T. “What Is Potential GDP and Why Does It Matter?” Federal Reserve Bank of St. Louis Economic Synopses, 2012,
No. 11, April 20, 2012.
Kliesen, Kevin L. “The NAIRU: Tailor-Made for the Fed?” Federal Reserve Bank of St. Louis Regional Economist, October 1999.
Lubik, Thomas and Slivinski, Stephen. “Is the Output Gap a Faulty Gauge for Monetary Policy?” Federal Reserve Bank of
Richmond Economic Brief EB10-01, January 2010.
Orphanides, Athanasios. “Monetary-Policy Rules and the Great Inflation.” American Economic Review, May 2002, 92(2),
pp. 115-20.
Orphanides, Athanasios. “The Quest for Prosperity Without Inflation.” Journal of Monetary Economics, April 2003, 50(3),
pp. 633-63.

Output gap: The difference between potential output and actual output.
Potential output: The real output (GDP) an economy can produce when it fully employs its available resources.
Actual output (real GDP): The amount that an economy actually produces, as measured by real GDP.

Page One Economics Newsletter from the Federal Reserve Bank of St. Louis continues the Liber8 Newsletter and provides an informative, accessible
economic essay written by our research analysts. A classroom edition is also available and includes a lesson plan written by our economic education
specialists. The newsletter is published 9 times per year, January through May and August through November.
Please visit our website and archives for more information and resources.
Views expressed do not necessarily reflect official positions of the Federal Reserve System.

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