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D OES A L OW-I NTEREST-R ATE
R EGIME H ARM S AVERS ?
James Bullard
President and CEO

Nonlinear Models in Macroeconomics and Finance for an
Unstable World
Norges Bank

Jan. 26, 2018
Oslo, Norway
Any opinions expressed here are the author’s and do not necessarily reflect those of the FOMC.

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Overview

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T HIS TALK

This academic talk was previously presented in London, UK, in
July 2017, in San Jose, Costa Rica, in August 2017, and at the
Advanced Workshop for Central Bankers—Northwestern
University, in September 2017.
The results here are preliminary and theoretical in nature.
Feedback is welcome.

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Low Interest Rates and Saving

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L OW INTEREST RATES AND SAVING

Since the 2007-2009 financial crisis and recession, real and
nominal interest rates in advanced economies have been
exceptionally low compared with postwar norms.
I call this a “low-interest-rate regime.”
A criticism of monetary policy in advanced economies following
the crisis has been that the low-interest-rate regime has been
detrimental for savers.
This presentation suggests that the low-interest-rate regime may
not be “harmful to savers.”

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L OW INTEREST RATES EMPIRICALLY

F IGURE : Source: Federal Reserve Board, U.S. Department of the Treasury,
Bank of England, European Central Bank and Japan’s Ministry of Finance.
Last observation: Jan. 22, 2018.

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T HE LINE OF ARGUMENT
In the model presented here, household credit markets will play
an essential role.
There are no “sticky prices.” Instead, the key friction in the
economy is non-state contingent nominal contracting (NSCNC) in
household credit markets.
Monetary policy will be able to repair this friction entirely by
using a version of nominal GDP targeting.
There will be an aggregate productivity shock following a
regime-switching stochastic process, yielding a
high-real-interest-rate and a low-real-interest-rate regime.
Main result: Under the optimal monetary policy, the allocation of
resources will be first-best intratemporally in either the high or the low
regime.
In this sense, a low-interest-rate regime will not be detrimental to
savers (or any other households).

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Credit Market Friction

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H OUSEHOLD CREDIT IN A DSGE MODEL

I study an economy with a large private credit market that is
essential to good macroeconomic performance.
If the household credit market is not working properly, some
households will consume much less than others.
The NSCNC friction means this market will not work well on its
own.
The role of monetary policy will be to repair this friction by
restoring complete markets.

I ignore ZLB issues in this talk. See the companion paper by
Azariadis, Bullard, Singh and Suda (2015), available on my web
page.

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I NCOME AND WEALTH INEQUALITY

There is a lot of income and wealth inequality in this stylized
model.
The role of credit markets, if they work correctly, will be to
reallocate uneven income across the life cycle into perfectly equal
per capita consumption.
The model equilibrium will naturally rank:
the wealth Gini coefficient > the income Gini coefficient > the
consumption Gini coefficient.

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H OW LARGE ARE THESE MARKETS ?

According to Mian and Sufi (AER, 2011), the ratio of household
debt to GDP in the U.S. was about 1.15 before it ballooned to
1.65 during the 2000s.
In today’s dollars, that would be equivalent to going from about
$19.5 trillion to about $28 trillion in household debt, comprised
mostly of mortgage debt.
Disrupting these markets might be quite costly for the economy,
so the NSCNC friction could be quite important.

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Environment

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S YMMETRY ASSUMPTIONS

I make a set of important “symmetry assumptions” so that we
can better understand the equilibrium of the model even with
substantial heterogeneity.
These assumptions involve the symmetry of the life cycle
productivity endowment pattern of the households, along with
log preferences, no discounting, and no population growth.
These assumptions help deliver the result that in the equilibrium
I study:
The real interest rate is exactly equal to the output growth rate at every
date, even in the stochastic economy.

This in turn creates a set of easy to understand baseline results
for this economy.

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L IFE CYCLE MODELS

General equilibrium life cycle economy = many-period
overlapping generations.
Key variables are privately-issued debt, real interest rates and
inflation.
Think of privately-issued debt = “mortgage-backed securities.”
This talk has inelastic labor supply. Elastic labor supply can be
added—for more on this, see the companion paper by Bullard
and Singh (2017), available on my web page.

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E NVIRONMENT DETAILS

The model is a standard T + 1-periods DSGE life-cycle
endowment economy.
A new generation of identical households is born at each date.
Households live for T + 1 periods. Any T 2 will work; I prefer
T + 1 = 241 (quarterly); odd values are convenient.
The monetary policymaker as controlling the price level P (t)
directly. For a more elaborate version with explicit money
demand, see Azariadis, Bullard, Singh, and Suda (2015).

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P REFERENCES
All participant households entering the economy at date t have
log preferences with no discounting
T

Vt = Et ∑ ln ct (t + j) ,
j=0

where ct (t + j) > 0 is the date t + j consumption of the
household born at date t.
Households that entered the economy at previous dates have
similar preferences and carry a net-asset-holding position into
date t. Households enter the economy and leave the economy
with zero net assets.
Other assumptions: Within-cohort agents are identical, no
population growth, no capital, no default, flexible prices, no
borrowing constraints.

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L IFE - CYCLE PRODUCTIVITY

All participant households are endowed with an identical
productivity profile over their lifetime.
The profile begins at a low value, rises to a peak in the middle
period of life, and then declines to the low value.
I assume the “low value” is bounded away from zero for this
talk.
The productivity profile is symmetric.
Agents can sell their productivity units available at date t in the
labor market at the competitive real wage.
The cross-sectional income distribution in the economy is this
profile multiplied by the real wage at that date.

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L IFE - CYCLE PRODUCTIVITY =

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CROSS SECTION

1 .0

0 .8

0 .6

0 .4

0 .2

50

100

150

200

F IGURE : A schematic productivity endowment profile for credit market
participants also represents the cross section of households at date t. The
profile is symmetric and peaks in the middle period of the life cycle. About
50 percent of the households earn 75 percent of the labor income in the credit
sector for η = 1.

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K EY FRICTION : NSCNC

Loans are dispersed and repaid in the unit of account—that is, in
nominal terms—and are not contingent on income realizations.
There are two aspects to this friction:
The non-state contingent aspect means that real allocations will be
perturbed by this friction, and
The nominal aspect means that the monetary authority may be able
to repair the distortion.

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S TOCHASTIC STRUCTURE

Aggregate real output is produced as Y (t) = Q (t) L (t), where
L (t) is the labor input and Q (t) is the level of technology.
The technology Q (t) improves at a stochastic rate λ (t, t + 1).
The competitive real wage per productivity unit, w (t) , is then
given by
w (t + 1) = λ (t, t + 1) w (t) ,
(1)
where w (0) > 0.
I will make assumptions concerning λ (t, t + 1) such that the
economy grows on average.

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R EGIME SWITCHING

I follow Bullard and Singh (IER, 2012, Section 2.4) to define a
two-state regime-switching process for λ.
There is a high-growth state with mean λH and a low-growth
state with mean λL , such that 1 < λL < λH .
Within each regime, there is additive noise described by σe (t),
where σ is a scale factor and e (t) i.i.d. N (0, 1).
A latent variable s (t) determines the regime and follows a
first-order Markov process.
The resulting process for λ (t, t + 1) can be written as an AR (1)
process with a nonstandard error term.

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T IMING PROTOCOL

At the beginning of date t, nature moves first and chooses
λ (t 1, t), which implies a value for w(t).
The policymaker moves next and chooses a value for the price
level, P (t).
Households then decide how much to consume and save.

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N OMINAL INTEREST RATE

Participant households contract by fixing the nominal interest
rate one period in advance.
The non-state contingent gross nominal interest rate, the contract
rate, is given by
Rn (t, t + 1)

1

= Et

ct ( t )
P (t)
.
ct ( t + 1 ) P ( t + 1 )

(2)

This rate depends on the expected gross rate of consumption
growth and the expected gross rate of inflation.
In the equilibrium I study, consumption growth rates are the
same for all households, so this condition is also the same for all
the households born at previous dates.

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C OMPLETE MARKETS WITH NSCNC
The countercyclical price level policy rule delivers complete
markets allocations:
P (t) =

Rn (t
λr (t

1, t)
P (t
1, t)

1) ,

(3)

where λr indicates a realization of the shock and Rn is the
expectation given in the previous slide.
This is similar to Sheedy (BPEA, 2014) and Koenig (IJCB, 2013).
Given this policy rule, households will consume equal amounts
of available production in the credit sector. This is “equity share
contracting,” which is optimal under homothetic preferences.
This price level rule renders the households’ date-t decision
problem deterministic because it perfectly insures the household
against future shocks to income.
Consumption and asset holdings fluctuate from period to
period, but in proportion to the value of w (t).

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S TATIONARY EQUILIBRIA

We let t 2 ( ∞, +∞).
We only consider stationary equilibria under the perfectly
credible policy rule governing P (t).
We let R (t) be the gross real rate of return in the credit market.
Stationary equilibrium is a sequence fR (t) , P (t)gt+=∞ ∞ such that
markets clear, households solve their optimization problems,
and the policymaker credibly adheres to the stated policy rule.
The key condition is that net aggregate asset holding, A (t), nets
out among participant households.

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Graphs

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L ABOR INCOME CHANGES IN CROSS SECTION

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F IGURE : How labor income changes across cohorts when the real wage
increases 10 percent for η = 1.

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N ET ASSET HOLDING IN CROSS SECTION
15
10
5

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5
10
15

F IGURE : Net asset holding by cohort along the complete markets balanced
growth path with η = 1. Borrowing, the negative values to the left, peaks at
stage 60 of the life cycle (age ~35), while positive assets peak at stage 180 of
the life cycle (age ~65). About 25 percent of the population holds about 75
percent of the assets.

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C HANGE IN NET ASSET HOLDING IN CROSS SECTION

20

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F IGURE : How net asset holding changes by cohort when the real wage
increases by 10 percent when η = 1.

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C ONSUMPTION IN CROSS SECTION
1 .0

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F IGURE : Schematic representation of consumption, the flat line, versus labor
income, the bell-shaped curve, by cohort along the complete markets
balanced growth path with w (t) = 1 and η = 1. The private credit market
completely solves the point-in-time income inequality problem.

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C HANGE IN CONSUMPTION IN CROSS SECTION

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F IGURE : How labor income and consumption change by cohort when the
real wage increases by 10 percent with η = 1.

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Complete Markets

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TARGETING

This economy could be mired in the low-interest-rate regime for
a long time, depending on assumptions concerning the
persistence of the productivity regimes.
Nevertheless, monetary policy can deliver first-best
intratemporal allocations via the price level rule described earlier
which induces “equity share contracting.” This occurs both with
regimes and across regimes.
The policymaker is completely mitigating the NSCNC friction and
restoring the Wicksellian natural rate of interest.
There is no sense in which savers are “hurt” in the
low-interest-rate regime (nor are borrowers “helped”).

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C AVEATS

The policymaker here is allowed to observe the shock and then
offset it with the appropriate setting for P (t). This is unrealistic,
but similar to baseline New Keynesian models in which
policymakers can appropriately offset incoming shocks.
The low-real-interest-rate regime is associated with a slower rate
of growth in real wages and real output. Households would
rather be in the higher growth regime in this sense. But the
productivity growth regime is taken as an exogenous process
chosen by nature here.
Monetary policy cannot switch the economy to the high-growth
regime, but it can conduct an optimal policy given the regime.
Monetary policy can be useful, but not so useful as to create high
real growth.

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M ORE CAVEATS

I focus on an equilibrium where the real interest rate equals the
output growth rate every period in the stochastic economy.
There may be other equilibria.
Results would still hold if there were two or more lifetime
productivity profiles, allowing for intracohort income inequality.

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I NACCURATE PERCEPTIONS OF REGIMES

In this presentation, the policymaker and the private sector
agents have rational expectations, meaning they understand the
nature of the regime-switching process driving the economy.
What if they had a misspecified model in which they expected
the economy to return to a fixed mean?
It remains for future reseach to understand how these results
may be altered in this scenario.
Nevertheless, this may be occurring in actual U.S. monetary
policy.
The following charts illustrate this possibility using recent U.S.
data.

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F IGURE : Source: Federal Reserve Board and author’s calculations. Last
observation: December 2017.

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P RIVATE SECTOR PERCEPTIONS

F IGURE : Source: FRB of Philadelphia and author’s calculations. Last
observation: 2017-Q3.

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C ONCLUSIONS

The desire behind many actual policy choices over the last
several years has been to help household credit markets,
especially mortgage markets, perform better.
The credit market here can be interpreted as a residential
mortgage market—“mortgage-backed securities.”
Monetary policy can alleviate the NSCNC friction and restore
the smooth functioning of the credit market.
This policy result remains even if the economy switches
infrequently between high- and low-real-interest-rate regimes.
One sentence summary: “One cannot read welfare implications
off of the observation of the real interest rate alone.”

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UNNATURAL REAL INTEREST RATES

Here the monetary policymaker can restore the first-best
intratemporal allocation of resources by moving the price level to
achieve the Wicksellian natural real rate of interest for the
economy, with the natural rate itself fluctuating according to a
regime-switching process.
This analysis can provide a good baseline for thinking about the
current situation in advanced economies if low real interest rates
can be mostly attributed to factors exogenous to monetary policy.
However, what if low real interest rates are attributed to monetary
policy itself (as many critics no doubt would argue)?
Then it may be the case that those rates are distortionary and could
hurt some segments of society. That could be analyzed here, say by
having the policymaker set the “wrong value for P (t)” each
period. That would require a computational solution as opposed to
the pencil-and-paper solution used in this talk.

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