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VOL. 12, NO. 11 • NOVEMBER 2017

DALLASFED

Economic
Letter
Fed’s Effective Lower Bound Constraint
on Monetary Policy Created Uncertainty
by Michael Plante, Alexander W. Richter and Nathaniel A. Throckmorton

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ABSTRACT: Uncertainty about
the economy increased when
the Fed reduced the federal
funds rate to its effective lower
bound because the constraint
restricted the Fed’s ability to
stabilize the economy. As
a result, a much stronger
negative relationship between
uncertainty and economic
activity emerged during
and shortly after the Great
Recession.

T

he financial crisis and subsequent recession compelled
the Fed to take unprecedented
action in December 2008.
Policymakers reduced the benchmark
federal funds rate to a range of 0 to 25
basis points (0.25 percentage points)—
the effective lower bound (ELB).
Reaching the ELB was important
because the federal funds rate is the
primary tool the Fed uses to implement
monetary policy, and pushing the rate so
low constrained the central bank’s ability to stabilize the economy and meet
its goal of full employment and price
stability.
Economists widely believe the ELB
can have significant negative implications for economic activity. However, the
ELB can also create uncertainty about the
future economy. Since the ELB prevents
the Fed from responding to unexpected
negative economic events with its traditional policy tool, those events more
severely affect the economy than in normal times. Uncertainty about the economy rises because people have a more
difficult time predicting future outcomes.
In many cases, uncertainty is viewed
as an outside factor that negatively affects
the economy. Uncertainty about tax and
spending policies—such as the debt ceiling or the sunset provision that could

have ended the George W. Bush-era tax
cuts—can delay investment decisions
and prompt consumers and firms to protect themselves from potentially negative
impacts. Such uncertainty, emanating
from external factors, is often referred to
as exogenous uncertainty.
By comparison, changes in uncertainty due to the ELB were caused by a severe
contraction in demand from consumers
and firms. In other words, uncertainty
arose in response to an event that was
endogenous to the economy, rather than
the impetus for the contraction.
Data indicate a strong negative
contemporaneous correlation between
uncertainty and real (inflation-adjusted)
gross domestic product (GDP) growth
emerged in late 2008 during the Great
Recession. Lagged real GDP growth also
became more tightly linked with current uncertainty, indicating that poor
economic conditions drove uncertainty.
Those findings are in line with what economic theory predicts when the ELB constrains the Fed. While the ELB was not
the only source of uncertainty during this
period, evidence suggests it was a major
contributing factor.

Empirical Measures of Uncertainty
Uncertainty is not directly observed
in the data, so economists and policy-

Economic Letter
makers use a variety of proxies to gauge
its level in the economy. One well-known
proxy is the VIX, which captures the riskneutral expected volatility in the S&P
500 stock market index over the coming
30 days. Another common measure is
the dispersion of individual economic
forecasts. The Survey of Professional
Forecasters (SPF) is a frequently cited
source that calculates the dispersion
in forecasts of various macroeconomic
variables.
These proxies suffer from a critical drawback: They may not reflect
uncertainty. For example, stock market
volatility can represent changes in leverage or risk aversion, and forecasters can
disagree even when they are confident in
their own projection.
Economists recently developed an
uncertainty index (abbreviated as JLN)
based on 132 macroeconomic time
series.1 The major advantage of this
index over other uncertainty proxies is
that it specifically attempts to measure
uncertainty. More precisely, it distinguishes between uncertainty—whether
indicators are more or less predictable—
and unconditional volatility.
Chart 1 plots the three measures of
uncertainty normalized to have zero
mean and unit variance—so they are
directly comparable—using data from

Chart

1

first quarter 1990 to fourth quarter 2016.
Although there is a connection between
the three series, it is not perfect, reflecting the fact that the two proxies can
vary for reasons besides changes in
uncertainty. However, all three measures sharply increased during the Great
Recession.

ELB and Uncertainty in Theory
A theoretical model provides a useful framework for learning how the
ELB impacts economic activity and
uncertainty.
The model, which is commonly
used in the monetary policy literature,
includes equations that describe how
households choose to spend and save,
how much labor they provide to the
private sector, how firms decide to set
prices and how a central bank such as
the Fed sets its policy rate. The equation
that describes the behavior of the central bank determines how strongly the
Fed adjusts its policy rate in response to
inflation and economic activity.2
The measure of uncertainty in the
model is based on the same statistic used
to calculate the macro uncertainty index.
Specifically, it equals the ex ante—or
forecasted—average volatility of real
GDP growth.
To understand this statistic better,

Uncertainty Increases Sharply During the Great Recession

Standard deviations
6
Expected stock market
volatility (VIX)
5
Forecast dispersion of
real GDP (SPF)
4
Macro Uncertainty Index
3
2
1
0
–1
–2
’90

’92

’94

’96

’98

’00

’02

’04

’06

’08

’10

’12

’14

’16

NOTES: Values are standard normalized using the entire time series. Shaded areas denote U.S. recessions.
SOURCES: Survey of Professional Forecasters; Chicago Board Options Exchange; “Measuring Uncertainty,” American
Economic Review; National Bureau of Economic Research.

2

suppose people are asked to predict
how much the economy will grow next
quarter. They would make use of the
information available to them and come
up with their best estimate. However, in
all likelihood, each person would factor
in uncertainty.
For example, if the most likely growth
rate is 2 percent, someone who is fairly
confident might predict real GDP growth
between 1.5 percent and 2.5 percent,
while someone who is more uncertain
might say 1 percent to 3 percent. A wider
average range implies higher expected
volatility of real GDP growth and, hence,
greater uncertainty.
Changes in aggregate demand play a
key role in bringing the economy to the
ELB and affecting uncertainty. One proxy
for changes in aggregate demand in our
model is the risk premium, which affects
the return on bonds, typically in excess
of the “safe” return Treasurys provide.
Chart 2A shows the relationship between
the risk premium and real GDP predicted
by the model. Both values are shown as
percent deviations from their long-run
values.
When the risk premium is elevated,
aggregate demand is lower because
households have a greater incentive to
save and postpone consumption. Firms
respond to the lower consumption
demand by decreasing their prices and
cutting production, so the lines in Chart
2A slope downward.
The Fed, as long as it is not constrained by the ELB, pursues its mandate
to stabilize prices and maintain full
employment by reducing its policy rate
in response to lower output and inflation. Usually, this mitigates the effects of
the lower demand. In situations when
the risk premium is extremely high and
demand is sufficiently low—as during the
Great Recession—the Fed is compelled
to reduce its policy rate to the ELB. At
that point, rate reductions are no longer
possible. The economy becomes more
sensitive to further declines in demand,
which leads to lower real GDP than if the
Fed was unconstrained. Thus, the slopes
in Chart 2A become steeper.
Chart 2B shows how the risk premium affects real GDP uncertainty.
When the policy rate is above its ELB,
the risk premium has little effect on the

Economic Letter • Federal Reserve Bank of Dallas • November 2017

Economic Letter
level of uncertainty. When it is near or
equal to its ELB, further increases in the
risk premium sharply increase real GDP
uncertainty.
To understand why, imagine several
people are trying to forecast real GDP
next quarter. Away from the ELB, the Fed
is able to help stabilize the economy, so
the range of plausible forecasts is relatively narrow. When the Fed loses that
ability due to the ELB, output is more
sensitive to shocks that hit the economy,
so the range of forecasts is much wider.
For example, when the risk premium
equals its long-run value, a 1 standard
deviation (+/–0.2 percent) change moves
real GDP by +/–0.4 percent. In contrast,
when the risk premium is 1.0 percent
above its long-run value, a +/–0.2 percent
change moves real GDP approximately
+/–1.1 percent. The broader range of
future output values translates into greater forecast error volatility and, hence,
higher uncertainty.
Chart 2C provides another way to
see how the ELB affects real GDP uncertainty by plotting the probability density
functions (PDF)—which illustrate the
likelihood of an event—for real GDP
next quarter, given three different values
for the risk premium. The values on the
horizontal axis are shown in deviations
from the mean forecast of real GDP.
The risk premium has little effect so
long as the ELB does not bind—in good
or normal times. In other words, the
dispersion in the forecasts is roughly the
same, regardless of the level of demand.
However, as the policy rate gets close to
and eventually hits the ELB (bad times),
the PDFs become flatter and skewed to
the left, reflecting a much higher level of
uncertainty.

mitigate some of the increased uncertainty that can accompany the ELB.
The theoretical model helps illustrate
how monetary policy affects uncertainty.
Suppose the policy rate is far from its ELB.
Chart 2A shows real GDP becomes less
sensitive to changes in the risk premium
(the slopes of the lines are flatter) when the
Fed more strongly responds to the infla-

Chart

2

The monetary policy response to economic changes also affects uncertainty
regardless of whether the ELB binds. For
example, theory predicts that in normal
times when the Fed is able to use its
traditional policy tool, a more aggressive
response to inflation leads to less uncertainty—not only about inflation but also
about the broader economy. Likewise,
when the ELB binds, a promise by the
Fed to more aggressively respond to
inflation after it raises its policy rate can

Effective Lower Bound Increases Uncertainty

A. Real GDP
Percent deviation from long-run value

3.0
1.5
0
–1.5

Weaker response to the inflation gap

–3.0

Stronger response to the inflation gap

–4.5
–6.0
–1.5

–1.2

–0.9

–0.6

–0.3
0
0.3
0.6
Risk premium
(percent deviation from long-run value)

0.9

1.2

1.5

B. Real GDP Uncertainty
Level of uncertainty

1.50
1.25

Weaker response to the inflation gap

1.00

Stronger response to the inflation gap

0.75
0.50
0.25
0
–1.5

–1.2

–0.9

–0.6

–0.3
0
0.3
0.6
Risk premium
(percent deviation from long-run value)

0.9

1.2

1.5

NOTE: Level of uncertainty measures the expected volatility of real GDP growth.

C. Probability Density Function
Density

1.25

Stronger Inflation Response

tion gap. The distribution of real GDP next
quarter becomes tighter around its expected value because there is less uncertainty
surrounding real GDP (Chart 2B).
When the ELB binds, the Fed is
able to reduce uncertainty by promising greater stability in the future, even
though it has no ability to directly influence outcomes in the current quarter.

Normal times (0% risk premium)
Good times (–1% risk premium)
Bad times (1% risk premium, ELB binds)

1.00
0.75
0.50
0.25
0

–4

–3

–2

–1

0

1

2

3

Real GDP next quarter
NOTE: For each curve, higher density values reflect greater chances of particular outcomes. Risk premiums are expressed
as a deviation from the long-run value.
SOURCE: Authors’ calculations.

Economic Letter • Federal Reserve Bank of Dallas • November 2017

3

Economic Letter

Table

1

Plante and Richter are senior economists
in the Research Department of the Federal
Reserve Bank of Dallas. Throckmorton is
an assistant professor of economics at the
College of William & Mary.

Stronger Correlations in the ELB Sample

A. Pre-ELB sample (first quarter 1986–third quarter 2008)
–3

–2

–1

0

1

2

3

VIX

–0.02

0.02

–0.12

–0.16

–0.13

–0.06

0.04

SPF

–0.22

–0.41

–0.39

–0.36

–0.18

–0.29

–0.10

JLN

–0.15

–0.35

–0.38

–0.47

–0.44

–0.46

–0.49

B. ELB sample (fourth quarter 2008–fourth quarter 2011)
–3

–2

–1

0

1

2

5

VIX

–0.24

–0.58

–0.73

–0.81

–0.66

–0.44

–0.09

SPF

–0.51

–0.66

–0.72

–0.53

–0.44

–0.25

–0.01

JLN

–0.86

–0.89

–0.85

–0.74

–0.62

–0.24

0.09

Notes
“Measuring Uncertainty,” by Kyle Jurado, Sydney C.
Ludvigson and Serena Ng, American Economic Review,
vol. 105, no. 3, March 2015, pp. 1177–1216.
2
For a complete description of the model as well as
additional results, see “The Zero Lower Bound and
Endogenous Uncertainty,” by Michael Plante, Alexander
W. Richter and Nathaniel A. Throckmorton, Economic
Journal, 2017, forthcoming.
1

NOTE: Correlations between current uncertainty and real GDP growth in the same period (0), previous or lagged periods
(–1, –2 and –3) and future or leading periods (1, 2 and 3).
SOURCES: Bureau of Economic Analysis; Survey of Professional Forecasters; Chicago Board Options Exchange;
“Measuring Uncertainty,” American Economic Review; authors’ calculations.

However, the Fed is not able to completely eliminate the increase in uncertainty.

Testing the Theory
The theoretical model tells us there
should be a tighter link between uncertainty and economic activity when the
ELB binds. Away from the ELB, real GDP
can vary a lot even though there is little
movement in uncertainty. At the ELB,
however, there is a strong negative relationship; a decrease in real GDP generally accompanies a sharp increase in
uncertainty.
Table 1 shows the contemporaneous
correlations—where 1 is perfectly correlated, –1 is perfectly negatively correlated
and 0 shows no correlation—between
the three measures of uncertainty and
real GDP growth, as well as the same cor-

DALLASFED

relations at leads and lags of real GDP
growth. Table 1A is based on the pre-ELB
sample, while Table 1B uses data from
when the Fed was most constrained—
before the effects of unconventional
policy.
A much stronger negative correlation
emerged when the federal funds rate
was stuck at its ELB. Most interestingly,
the correlations with lags of real GDP
growth became stronger, while the correlations with leads of real GDP growth
were either weaker or unchanged in the
ELB sample.
The results show that periods of high
uncertainty do not necessarily mean
uncertainty is having a large effect on
economic activity. At the ELB, changes
in uncertainty are mostly a byproduct of
what is going on in the economy.

Economic Letter

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