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VOL. 12, NO. 2 • FEBRUARY 2017

DALLASFED

Economic
Letter
Navigating by the Stars: The Natural
Rate as Economic Forecasting Tool
by Evan F. Koenig and Alan Armen

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ABSTRACT: Fed policymakers
must assess the stance of
monetary policy each time
they decide whether the target
federal funds rate should be
changed. Several different
benchmark, or “natural,”
interest rates have been
suggested for this purpose.
The gap between the target
funds rate and the natural
rate should, in principle, help
forecast real economic activity
and inflation.

F

ederal Reserve policymakers
adjust the overnight interbank
lending rate—the federal funds
rate—in an effort to satisfy the
Fed’s mandate to promote full employment and price stability. So it is important
that they understand how the funds rate
affects unemployment and inflation. One
approach is to compare the level of the
real (inflation-adjusted) funds rate to a
“natural,” “neutral” or “equilibrium” rate
of interest. This reference interest rate is
often called “r star” and is labeled r*.
A real funds rate above r* indicates

Chart

1

that monetary policy is restrictive, tending
to drive the unemployment rate up and
inflation down. A real funds rate below r*
indicates that policy is accommodative,
tending to drive the unemployment rate
down and inflation up.
We examine three alternative empirical
estimates of r* to see which is most useful
for assessing the Federal Reserve’s policy
stance. The measure that seems to perform
best is a simple combination of a longterm interest rate and growth in household
net worth. It suggests that recent policy has
been accommodative, which means that

Natural-Rate Estimates Differ Greatly in Trend, Variability

Percent

Real-time data begin

8
6
4
2
0
2 percent fixed
neutral rate
(Taylor rule)

–2
–4

Laubach–Williams
neutral real rate

–6
–8

Koenig–Armen
neutral real rate

1985

1990

1995

2000

2005

2010

2015

NOTE: Shaded bars indicate U.S. recessions.
SOURCES: Laubach and Williams (2003); Koenig and Armen (2015); National Bureau of Economic Research.

Economic Letter
Chart

2

Koenig–Armen Funds-Rate Gap Has Strongest
Relationship with Unemployment Rate

Financial crisis
Postcrisis
Fitted line, 1985:Q1–2016:Q2

3

0.5

1

–0.5

0

–1.5

–1
–2

–4

–2
0
2
4
6
Tight policy
Easy policy
Real funds rate minus 2 percent, lagged
four quarters (pct. points)*

8

B. Laubach–Williams
Four-quarter change in unemployment rate (pct. points)
5
Precrisis

Financial crisis
Postcrisis
Fitted line, 1985:Q1–2016:Q2

4
3

–3.5

–4

–2
0
2
4
6
8
Tight policy
Easy policy
Real funds rate minus 2 percent, lagged
four quarters (pct. points)**
B. Laubach–Williams
Four-quarter change in output gap (pct. points)*
2.5
Correlation = –0.42
1.5

–0.5

1

Precrisis
Financial crisis
Postcrisis
Fitted line,
1985:Q1–2016:Q2

–1.5

0
–1

–2.5

Correlation = 0.22
–6

–4

–2
0
2
4
6
8
Tight policy
Easy policy
Real funds rate minus Laubach–Williams real time
1-sided neutral real rate, lagged four quarters (pct. points)*

C. Koenig–Armen
Four-quarter change in unemployment rate (pct. points)
5
Precrisis
3
2

–3.5

0

–1.5

–2
0
2
4
6
Tight policy
Easy policy
Real funds rate minus Koenig–Armen neutral real rate,
lagged four quarters (pct. points)*

Precrisis
Financial crisis
Postcrisis
Fitted line,
1985:Q1–2016:Q2

–2.5

Correlation = 0.72
–4

–2
0
2
4
6
8
Tight policy
Easy policy
Real funds rate minus Laubach–Williams real time 1-sided
neutral real rate, lagged four quarters (pct. points)**

0.5

1

–6

–4

1.5

–0.5

–1

–6

C. Koenig–Armen
Four-quarter change in output gap (pct. points)*
2.5
Correlation = –0.47

Financial crisis
Postcrisis
Fitted line,
1985:Q1–2016:Q2

4

–2

–6

0.5

2

–2

Precrisis
Financial crisis
Postcrisis
Fitted line,
1985:Q1–2016:Q2

–2.5

Correlation = 0.36
–6

All Three Policy Measures Lead the Output Gap

1.5

2

8

*Real rates are computed with the projected four-quarter-ahead, four-quarter percent change in
the first-revision core personal consumption expenditures price index, as described in Laubach
and Williams (2003).

–3.5

–6

–4
–2
0
2
4
6
Tight policy
Easy policy
Real funds rate minus Koenig–Armen neutral real rate,
lagged four quarters (pct. points)**

8

*Percentage-point deviations of real GDP from two-sided Laubach and Williams (2003) estimates
of potential real GDP.

NOTES: Yellow diamonds correspond to the four quarters immediately following the collapse of
Lehman Brothers. Correlation statistic and regression for fitted line exclude 2008:Q4–2009:Q3.

**Real rates are computed with the projected four-quarter-ahead, four-quarter percent change in
the first-revision core personal consumption expenditures price index, as described in Laubach
and Williams (2003).

SOURCES: Bureau of Economic Analysis; Bureau of Labor Statistics; Koenig and Armen (2015);
Laubach and Williams (2003); authors’ calculations.

SOURCES: Bureau of Economic Analysis; Koenig and Armen (2015); Laubach and Williams
(2003); authors’ calculations.

the unemployment rate is likely to fall in coming quarters and inflation is likely to rise.

What Is r*?
In most macroeconomic models, there is a negative relationship—called the IS curve—between the real interest rate and the
short-run level of output.1 In these models, r* is the real interest rate

2

3

A. Fixed neutral rate
Four-quarter change in output gap (pct. points)*
2.5
Correlation = –0.39

A. Fixed neutral rate
Four-quarter change in unemployment rate (pct. points)
5
Precrisis
4

Chart

that is consistent with the economy operating at the full-employment level of output, y*.
The Federal Reserve, by adjusting the real funds rate, moves
the economy along the IS curve, increasing or decreasing
output, y, relative to y*. A real funds rate that is low relative to
r* stimulates output and employment by encouraging households to consume now rather than later, and by encouraging

Economic Letter • Federal Reserve Bank of Dallas • February 2017

Economic Letter
businesses to expand investment. A real funds rate that is high
relative to r* restrains output and employment by discouraging
consumption and investment.
Increases (decreases) in output relative to y*, in turn, put upward
(downward) pressure on inflation relative to recent past inflation or
longer-run inflation expectations.
This discussion overly simplifies the conduct of policy. For one
thing, the economy does not typically respond contemporaneously
to policy shifts.2 Also, r* isn’t directly observed: Its value must be
inferred from the behaviors of output, unemployment, inflation and
other macroeconomic variables. This inference could go wrong in
many ways.
Presumably, though, the better the estimate of r*, the tighter will
be the links between the stance of policy, as measured by the deviation of the real funds rate from r*, and the strength of the economy.
One should observe weaker real activity and lower inflation in
response to restrictive policy, and stronger real activity and higher
inflation in response to accommodative policy.

Alternative r* Measures
The first neutral rate that we consider is a simple, fixed value.
This approach isn’t without precedent. The celebrated Taylor rule—
Stanford University economist John B. Taylor’s guide for setting the
funds rate—assumes that policy is, on average, restrictive when the
real funds rate is above 2 percent and is, on average, accommodative
when the real funds rate is below 2 percent.3 We find that 2 percent
is a reasonable estimate of the neutral rate in the pre-financial-crisis
period, if the neutral rate is assumed fixed.4
A time-varying neutral-rate estimate was developed by Thomas
Laubach and John C. Williams (LW). They infer values for both
r* and potential output using a dynamic IS-curve framework that
relates the output gap, y – y*, to past output gaps and past policy
gaps, r – r*.5 Additionally, LW assume that the best forecast of future
trend output growth is current trend growth and that r* is positively
related to trend growth. Thus, in contrast with Taylor, who assumes
that r* is well approximated by a constant, LW assume that r* shows
no tendency to revert to any particular value over time.
Like Laubach and Williams, Koenig and Armen (KA) estimate
r* within a dynamic IS-curve framework.6 However, rather than
define the IS curve as a relationship between the output and policy
gaps, KA define it as a relationship between unemployment and
policy gaps.
The unemployment gap, which is the difference between the
equilibrium (“natural”) rate of unemployment, u*, and the actual
rate of unemployment, u, has several advantages over the output
gap. First, the unemployment gap is more directly related to the
Fed’s mandate to promote full employment. Second, unemployment
data are released earlier and are subject to less revision than output
data. Finally, while neither potential output nor the natural rate of
unemployment is directly observed, u* is reasonably approximated
by a constant, whereas y* is not.
Another difference between LW and KA is that while LW posit a
relationship between the neutral real interest rate and trend growth
in potential output, KA posit a relationship between the neutral
nominal interest rate and two financial variables: a long-forward
interest rate and growth in household net worth.
Intuitively, banks find it profitable to accept new deposits and

Chart

4

Only the Koenig–Armen Funds-Rate Gap
Leads Inflation

A. Fixed neutral rate
Four-quarter change in four-quarter Trimmed Mean PCE inflation
(pct. points)
1.5
Precrisis

Financial crisis
Postcrisis
Fitted line,
1985:Q1–2016:Q2

1.0
0.5
0

–0.5
–1.0
–1.5

Correlation = 0.00
–6

–4

–2

0

2

4

6

Tight policy

Easy policy

8

Real funds rate minus 2 percent, lagged
four quarters (pct. points)*
B. Laubach–Williams
Four-quarter change in four-quarter Trimmed Mean PCE inflation
(pct. points)
1.5
Precrisis

Financial crisis
Postcrisis
Fitted line,
1985:Q1–2016:Q2

1.0
0.5
0
–0.5
–1.0
–1.5

Correlation = 0.04
–6

–4

–2
Easy policy

0

2

4
Tight policy

6

8

Real funds rate minus Laubach–Williams real-time
1-sided neutral real rate, lagged four quarters (pct. points)*
C. Koenig–Armen
Four-quarter change in four-quarter Trimmed Mean PCE inflation
(pct. points)
1.5
Precrisis
Correlation = –0.48

Financial crisis
Postcrisis
Fitted line,
1985:Q1–2016:Q2

1.0
0.5
0
–0.5
–1.0
–1.5

–6

–4

–2

0

Easy policy

2

4

Tight policy

6

8

Real funds rate minus Koenig–Armen neutral real rate,
lagged four quarters (pct. points)*
*Real rates are computed with the projected four-quarter-ahead, four-quarter percent change
in the first-revision core personal consumption expenditures (PCE) price index, as described in
Laubach and Williams (2003).
SOURCES: Bureau of Economic Analysis; Federal Reserve Bank of Dallas; Koenig and Armen
(2015); Laubach and Williams (2003); authors’ calculations.

expand lending when long-term interest rates are high relative
to short-term rates. Increases in net worth expand households’
borrowing capacity. The notion that increases in wealth encourage consumption, shifting the IS curve upward (or to the right),
has long been recognized.7
The LW and KA neutral rates appear to share a common
long-run trend—a conclusion confirmed by statistical analysis
(Chart 1). However, the KA measure is much more volatile, and
deviations of the KA neutral rate away from the LW neutral rate
are strongly procyclical. This raises the question of whether the

Economic Letter • Federal Reserve Bank of Dallas • February 2017

3

Economic Letter

longer-term variation shared by the KA
and LW r* estimates and the shorter-term
swings unique to the KA measure contain
useful information about future real activity
and/or future inflation.

Forecasting Unemployment
All three policy measures have predictive power for four-quarter changes in the
unemployment rate, with restrictive policy
(r > r*) tending to precede increases in the
unemployment rate, and accommodative
policy (r < r*) tending to precede decreases
in the unemployment rate (Chart 2). The
strength of the relationship between policy
and future movements in the unemployment rate varies considerably, though,
depending on which neutral-rate estimate
is used. The weakest link is with the LW
measure of monetary policy; the strongest
link is with the KA measure. The measure
of policy restrictiveness implicit in the
Taylor rule is between the two.
Follow-up regression analysis using all
three policy-gap measures shows that the
KA interest rate gap dominates the alternatives in real-time forecasting of the unemployment rate.

Output Gap, Inflation
The Taylor policy measure, which
assumes r* = 2, does about as well predicting four-quarter changes in the output gap
as it does predicting four-quarter changes
in the unemployment rate (Chart 3). The
LW policy gap, in contrast, does notably
better. Although the performance of the KA
policy gap deteriorates, it still outperforms
the other two policy measures.
A regression analysis that includes all
three policy measures finds that the LW

DALLASFED

and KA measures both have predictive
power, with neither dominating the other.
In contrast, the policy gap that assumes a
fixed, 2 percent neutral rate lacks significant predictive power.
Contrary to expectations, neither the
fixed r* measure of policy nor the LW
measure has any correlation with future
changes in Trimmed Mean PCE (personal
consumption expenditures) inflation
(Chart 4). In contrast, policy that is restrictive according to the KA measure tends
to be followed by a reduction in inflation,
while policy that is accommodative tends
to be followed by an inflation increase.
In a regression that includes all three
policy measures, only the KA interest rate
gap is statistically significant.

Current Policy
The nominal federal funds rate stood at
0.4 percent and projected core PCE inflation at 1.6 percent in third quarter 2016;
thus, the real funds rate was 0.4 – 1.6 = −1.2
percent. Against a fixed 2 percent neutral
rate, policy was highly accommodative:
r – r* = −1.2 – 2.0 = −3.2 percentage points.
The LW and KA neutral-rate estimates were 0.2 percent and −0.1 percent,
respectively, in the third quarter of 2016.
The corresponding policy gaps were
−1.2 – 0.2 = −1.4 and −1.2 + 0.1 = −1.1 percentage points. By either measure, policy
was accommodative but not nearly so
much as in the fixed-r* framework.
Charts 2C and 4C indicate that a KA
rate gap of −1.1 percentage points has
typically been associated with a 0.2-percentage-point decline in the unemployment rate over four quarters (which would
lower the jobless rate to 4.7 percent in

Economic Letter

is published by the Federal Reserve Bank of Dallas.
The views expressed are those of the authors and
should not be attributed to the Federal Reserve Bank
of Dallas or the Federal Reserve System.
Articles may be reprinted on the condition that
the source is credited to the Federal Reserve Bank
of Dallas.
Economic Letter is available on the Dallas Fed
website, www.dallasfed.org.

third quarter 2017) and a 0.1-percentagepoint increase in inflation (which would
raise inflation to 1.8 percent per year). The
uncertainty around these estimates is large.
Koenig is senior vice president and
principal policy advisor and Armen is a
senior research analyst in the Research
Department at the Federal Reserve Bank
of Dallas.

Notes
See Macroeconomics by N. Gregory Mankiw, New York:
Worth Publishers, 1992, and “Rethinking the IS in IS-LM:
Adapting Keynesian Tools to Non-Keynesian Economies,”
by Evan F. Koenig, Federal Reserve Bank of Dallas Economic
Review, Third Quarter, 1993, and Fourth Quarter, 1993.
2
Modern theory suggests that the economy may respond
with a lag to unexpected shifts in policy and may move in
advance of anticipated policy changes.
3
See “Discretion Versus Policy Rules in Practice,” by John
B. Taylor, Carnegie Rochester Conference Series on Public
Policy, vol. 39, no. 1, 1993, pp. 195–214.
4
When we estimate an IS-style equation over the precrisis
period and assume a fixed r*, the point estimate of r* is
within one standard error of 2 percent.
5
See “Measuring the Natural Rate of Interest,” by Thomas
Laubach and John C. Williams, Review of Economics and
Statistics, vol. 85, no. 4, 2003, pp. 1,063–70.
6
See “Assessing Monetary Accommodation: A Simple
Empirical Model of Monetary Policy and Its Implications for
Unemployment and Inflation,” by Evan F. Koenig and Alan
Armen, Federal Reserve Bank of Dallas Staff Papers, no. 23,
December 2015.
7
See “The Classical Stationary State,” by Arthur C. Pigou,
Economic Journal, vol. 53, 1943, pp. 343–51. Some
researchers recognize that changing credit conditions
cause IS-curve shifts but define r* to exclude the effects
of those shifts. See “What Can the Data Tell Us About the
Equilibrium Real Interest Rate?” by Michael T. Kiley, Finance
and Economics Discussion Series, no. 2015-077, Federal
Reserve Board, 2015.
1

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