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St. Louis Fed's Bullard Releases Study on Optimal
Monetary Policy at the Zero Lower Bound
May 28, 2015
ST. LOUIS – In a new research working paper released today, Federal Reserve Bank of St.
Louis President James Bullard examines options for optimal monetary policy when the
short-term nominal interest rate targeted by monetary policymakers (the policy rate)
remains effectively at zero.
The paper, titled “Optimal Monetary Policy at the Zero Lower Bound,” was co-authored with
Costas Azariadis of Washington University in St. Louis and the Federal Reserve Bank of St.
Louis, Aarti Singh of the University of Sydney, and Jacek Suda of the Narodowy Bank Polski.
In the aftermath of the �nancial crisis, the Federal Reserve used forward guidance and
quantitative easing to provide further accommodation once the policy rate hit zero. Bullard
noted that quantitative easing, which consists of buying publicly-issued and privately-issued
debt, seems to be effective in the empirical literature but not in the theoretical literature.
With forward guidance, the central bank promises to stay at zero even longer than it
otherwise would. According to conventional theory, forward guidance should lead to higher
growth and also to higher expected and actual in�ation.
Expanding further on the paper, Bullard noted that while the U.S. policy rate has been near
zero for 6.5 years and forward guidance has been used, there has not been a boom in the
economy. “It’s time to question the current theory and explore other models about what is
going on at the zero lower bound,” he said. Our current models can miss a big part of the
story, including the importance of smoothly operating credit markets.
“The �nancial crisis was about credit market problems,” he said. “But most of the models
that have been used regarding forward guidance and quantitative easing do not include
credit markets.”
In their new academic model, Bullard and his co-authors construct a credit market that
plays a crucial role in how the economy operates. They examine how monetary policy can �x
credit market imperfections, both in normal times and in times when the zero lower bound
is encountered. In the latter case, this can be done by promising an increase in the price

level in the following period suf�cient to prevent reaching the zero lower bound. Further, the
authors found that forward guidance was not a good policy choice in their model, and that it
was unclear how quantitative easing could be used to engineer a complete market allocation
when the zero bound threatens. Since the policy implications of the model appear to be quite
different from current policy, they encourage future research.
Credit Markets and the Role of Monetary Policy
Their model examines two types of households: Credit market participants (“credit users”),
who borrow and save over the life cycle, and credit market non-participants (“cash users”),
who work only every other period and want to consume when they are not working. Among
the credit market participants, middle-aged households are in their peak earning years,
while younger and older households do not have much income. Younger households borrow
on net, and the middle households save for retirement and lend to the younger households.
In this credit market, debts are in the form of “non-state contingent nominal contracts.” That
is, contracts are written in dollar terms and do not depend on whether the economy is
experiencing high or low growth. According to economic theory, however, loans should be
state-contingent. In other words, Bullard explained that a borrower would pay back more if
the economy had a good year and less in a bad year. He noted that we don’t see this in reality,
meaning that the credit market is inef�cient and does not share risk appropriately between
borrowers and lenders.
What is the role of monetary policy, according to this model? “Because the contracts are
written in dollar terms, the central bank can change the price level every period by supplying
currency to cash users in order to get the right amount of state contingency in this credit
market,” Bullard said, adding that this policy is very close to nominal GDP targeting.
“In normal times (away from the zero lower bound), monetary policy can mitigate the
friction appropriately and thus ensure a smoothly operating (complete) credit market,”
Bullard and his co-authors wrote. The credit market plays a role in transforming the uneven
income into perfectly equal consumption across all credit market participants. The authors
noted that this policy will work well for shocks that are small enough that the nominal
interest rate remains positive.
In this model, the policymaker’s primary objective is to ensure the credit market is working
smoothly. The secondary objective is to keep in�ation relatively low by hitting an in�ation
target on average so as not to harm the cash users too much. Bullard noted that, in normal
times, the policymaker will be able to achieve both of these goals, but what happens during a
time when the zero lower bound is encountered and threatens to bind?
Zero Lower Bound

Bullard explained that the zero lower bound would threaten to bind in the event of a major
negative economic shock, such as a deep and persistent recession. “What is the policymaker
to do in this circumstance, if the objective is to maintain smoothly operating credit
markets?” Bullard and his co-authors asked.
In this scenario, “The monetary policymaker can still maintain a complete credit market by
having a one-time, or special, increase in the price level,” Bullard said. As stated in the paper,
“This keeps the nominal interest rate positive and maintains the complete market
allocations for credit market participant households.” However, the authors noted that this
policy does have a drawback: “The price level increase harms cash-using households
relative to policy away from the zero lower bound.”
Bullard noted that forward guidance is not a good policy in this model. Instead, the
policymaker would want to take action to make sure the policy rate is not zero. While
quantitative easing can be implemented in the model by purchasing privately-issued debt of
the younger households, Bullard said it was unclear how the central bank could use
quantitative easing to try to complete the credit market.
“This is a very different set of results compared to what has dominated thinking in monetary
policy in the last �ve years. Our results might help to inform the debate on the topic of
optimal monetary policy at the zero lower bound,” Bullard said.
He cautioned against drawing strong policy implications from this theoretical model. Given
that the policy conclusions are quite a bit different from those in a standard sticky price New
Keynesian model, Bullard stressed the importance of more research on different types of
models to see what they recommend in terms of monetary policy at the zero lower bound.