1. Introduction
In this note, we analyze an implication of the effective lower bound (ELB) risk--the possibility that adverse shocks will force policymakers in the future to lower the policy rate to the ELB--on inflation dynamics after liftoff. The implication we analyze is deflationary bias--a phenomenon in which the tail risk induced by the ELB constraint leads inflation to decline under conventional monetary policy rules. In particular, our focus is examining how large the deflationary bias is at the economy's risky steady state--the point to which the economy eventually converges as headwinds and tailwinds dissipate.

We first document, briefly, how academic economists, policymakers, and financial market participants assess the ELB risk. We then use an empirically rich DSGE (Dynamic Stochastic General Equilibrium) model to analyze how large the deflationary bias induced by the ELB risk might be in the U.S. Our baseline simulation suggests that the ELB risk causes inflation to undershoot the target rate of 2 percent by about 20 basis points at the economy's risky steady state under an empirically plausible specification of monetary policy. We find that the deflationary bias induced by the ELB risk can increase to as large as 40 basis points under alternative plausible assumptions regarding the long-run equilibrium real rate.

Overall, our result provides a cautionary tale for policymakers aiming to raise inflation from currently low levels: Even after liftoff, the ELB constraint can have enduring adverse effects on inflation through its effects on expectations. The note concludes by briefly discussing some implications of this enduring effect of the ELB constraint for monetary policy strategy. The analyses in this note draw heavily on Hills, Nakata, and Schmidt (2016).

2. ELB risk after lift-off
Academic economists and policymakers have noted that the ELB is not likely to be a one-time event. Ball (2013) argues that, if the inflation target remains 2 percent, "the lower bound on interest rates is likely to constrain monetary policy in a large fraction of recessions" in the U.S. In its April 2014 WEO, the IMF extensively studies the world wide decline in equilibrium real rates and states that the probability of hitting the ELB is likely to increase going forward (IMF (2014)). A renewed interest in the analysis of optimal inflation targets and alternative monetary policy frameworks is based on the assumption that the ELB can bind again (Blanchard et al. (2010) and Bernanke (2015)).

Financial market participants also see the ELB binding again in the future as a quantitatively significant possibility. According to a special question in the Survey of Primary Dealers on December 2015, a median respondent attached 20 percent probability to the event that the federal funds rate returns to the ELB within two years after lift-off.

3. An implication of the ELB risk: Deflationary bias
3.1. What is deflationary bias?
When firms are forward-looking in their pricing decisions, the ELB risk leads inflation to fall below the inflation target at the economy's risky steady state, provided that monetary policy is characterized by a standard interest-rate feedback rule. In plain English, this means that inflation will return to a level below the inflation target when all headwinds or tailwinds dissipate. This also means that inflation fluctuates around that level even in absence of actual ELB episodes. This phenomenon occurs because forward-looking firms base their pricing decisions on the expected economic conditions in the future, and the tail risk induced by the ELB constraint lowers the expected economic conditions. In the academic literature, this phenomenon is referred to as deflationary bias.³

3.2. How large is the deflationary bias?
We use an empirically rich DSGE model calibrated to broadly match key moments of the output gap, inflation, and the federal funds rate in the U.S. over the last two decades to get some sense of how large the deflationary bias may be in reality. The model is a standard New Keynesian model augmented with consumption habits in the household's preference, sticky wages, and an interest-rate smoothing term in the policy rule. There are two shocks---productivity and demand shocks. The main shock that drives fluctuations in this economy is the demand shock, which is implemented through time-varying discount rates.⁴

The inflation target in the model's interest-rate feedback rule is set to 2 percent. The steady-state discount rate and the growth rate of total factor productivity are chosen so that the deterministic steady-state policy rate is 3.75 percent. The effective lower bound on the federal funds rate is set to 13 basis points. The list of parameter values is in Hills, Nakata, and Schmidt (2016). The model is solved globally using a nonlinear solution method.⁵

The first three rows in Table 1 show the unconditional standard deviations of inflation, the output gap and the nominal interest rate from the model and from the data. The standard deviations of the output gap, inflation, and the policy rate in the model are very close to those in the data (3.1, 0.42, and 2.34 in the model versus 2.9, 0.52, and 2.34 in the data). The next two rows in Table 1 show the conditional mean of the output gap and inflation when the policy rate is at the ELB from the model and from the data. The conditional means of the output gap and inflation are somewhat higher and lower than those in the data, but are reasonably close. Finally, the frequency of being at the ELB and the expected duration of the ELB episode are 16 percent and 9 quarters in the model, versus 36 percent and 26 quarters in the data.⁶

Table 2 compares the deterministic and risky steady states of inflation, the output gap, and the policy rate. Due to the deflationary bias explained earlier, inflation is lower at the risky steady state than at the deterministic steady state Inflation is about 30 basis points lower at the risky steady state than the target rate of 2 percent. The policy rate is lower at the risky steady state than the deterministic steady state (3.04 percent versus 3.75 percent), as a lower inflation is associated with a lower policy rate in the interest-rate feedback rule.⁷ The expected real rate is lower at the risky steady state, and thus the output gap is positive at the risky steady state, albeit slightly.

Since the ELB constraint is not the only nonlinear feature of the model, there is some difference between the deterministic and risky steady states even in the absence of the ELB constraint, as shown in the last two rows of Table 2. For inflation, the risky steady state is 1.88 percent in the model without the ELB constraint. The contribution of the ELB risk to the overall deflationary bias at the risky steady state is 17 basis points. Thus, the majority of the overall deflationary bias in the model with the ELB constraint comes from the ELB constraint, instead of other nonlinearities of the model.

Note that the risky steady state is conceptually different from the average. Let's take inflation as an example. The risky steady state inflation is the point around which inflation fluctuates, while the average inflation is the average of inflation in all states of the economy. As shown in Table 2 and Figure 1, the risky steady state inflation is higher than the average inflation in the economy with the ELB constraint, as the ELB constraint makes the unconditional distribution of inflation negatively skewed. The observation that the ELB constraint pushes down the average inflation below the target by creating asymmetry in the distribution of inflation is intuitive and has been well known for a long time (Coenen, Orphanides, and Wieland (2004) and Reifschneider and Williams (2000)). This holds true even when price-setters form expectations in a backward-looking manner. The result that the ELB risk lowers the center of the distribution below the target is less intuitive and requires that price-setters are forward-looking in forming their expectations.

Figure 1: Unconditional Distribution of Inflation

Note: Authors' calculation as described in Hills, Nakata, and Schmidt (2016)

Accessible version

To emphasize the fact that the possibility of the ELB is the source of the deflationary bias, we contrast the impulse response functions of inflation, output, and the policy rate from the model with those from a perfect-foresight version of the model, which ignores the ELB risk. Figure 2 shows the impulse response functions when the initial demand and productivity shocks are chosen so that inflation is 50 basis points, the output gap is -7 percent, and the policy rate is at the ELB at period one. Black lines are from the perfect-foresight version of the model that abstracts from the ELB risk, while red lines are from the model that correctly takes the ELB risk into account. Under perfect-foresight, the policy rate stays at the ELB for 11 quarters and will gradually converge to 3.75 percent. Inflation slowly rises to 2 percent, and the output gap will converge to zero after some overshooting. On the other hand, when the private sector correctly acknowledges the ELB risk, the policy rate stays at the ELB for 13 quarters and returns to its risky steady state of about 3 percent. Inflation slowly rises to about 1.7 percent and the output gap remains slightly positive in the long run.

Figure 2: The Effect of the ELB Risk on Projections

Note: Authors' calculation as described in Hills, Nakata, and Schmidt (2016)

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3.3. The long-run equilibrium interest rate and deflationary bias
The magnitude of the deflationary bias depends importantly on the frequency of the policy rate being at the ELB, which in turn depends on the long-run equilibrium policy rate. Figure 3 shows how the magnitude of deflationary bias depends on the (deterministic) steady-state level of the policy rate. In this figure, we vary the parameter governing the long-run growth rate of labor productivity to induce the change in the steady-state policy rate. As demonstrated in the top-right panel, deflationary bias is larger when the deterministic steady state policy rate is lower. This is because the probability of hitting the ELB is higher with a lower steady-state policy rate, as shown in the top-left panel of the figure. When the deterministic steady state policy rate is 3.35 percent, the probability of being at the ELB is 28 percent and inflation is about 50 basis points below the inflation target at the economy's risky steady state. Comparing this deflationary bias with that in the model without the ELB constraint, indicated by the dashed black line, shows that the ELB risk accounts for about 40 basis points of the overall deflationary bias.⁸

Figure 3: Long-Run Policy Rate and Deflationary Bias

Note: Authors' calculation as described in Hills, Nakata, and Schmidt (2016)

Accessible version

4. Concluding remarks
This note has demonstrated that the deflationary bias induced by the ELB risk is non-trivial in an empirically rich DSGE model calibrated to match key features of the U.S. economy. The result that the ELB constraint has enduring effects on the economy even after liftoff has important implications for the design of monetary policy. For example, the deflationary bias, while typically ignored in the analyses of optimal inflation targets, importantly affects the cost-benefit calculation of changing the inflation target. As another example, Nakata and Schmidt (2014) show that the deflationary bias makes it desirable for the central bank to put more weight on the inflation stabilization objective, relative to the output stabilization objective.⁹

This conclusion is of course conditional on the validity of the model used for the analysis. While the model is a variant of the standard model widely used at central banks, there is a continuing debate about the usefulness of this model for policy analysis among economists. Thus, caution is needed when drawing policy implications.¹⁰

References:

Adam, K., and R. Billi (2007): "Discretionary Monetary Policy and the Zero Lower Bound on Nominal Interest Rates," Journal of Monetary Economics, 54(3), 728-752.

Ball, L. M. (2013): "The Case for Four Percent Inflation," Central Bank Review, 13, 17-31.

Bernanke, B. (2015): "Monetary Policy in the Future," Remarks at the Rethinking Macro Policy III Conference at the IMF, Washington, DC.

Blanchard, O., G. Dell'Ariccia, and P. Mauro (2010): "Rethinking Macroeconomic Policy," Journal of Money, Credit, and Banking, 42(s1), 199-215.

Chung, H., E. Herbst, and M. T. Kiley (2014): "Effective Monetary Policy Strategies in New Keynesian Models: A Re-Examination," NBER Working Papers 20611, National Bureau of Economic Research.

Coenen, G., A. Orphanides, and V. Wieland (2004): "Price Stability and Monetary Policy Effectiveness when Nominal Interest Rates are Bounded at Zero," B.E. Journal of Macroeconomics: Advances in Macroeconomics, 4(1).

Evans, C., J. Fisher, F. Gourio, and S. Krane (2015): "Risk Management for Monetary Policy Near the Zero Lower Bound," Brookings Papers on Economic Activity Conference Draft.

Hills, T. S., T. Nakata, and S. Schmidt (2016): "The Risky Steady State and the Interest Rate Lower Bound," Finance and Economics Discussion Series 2016-009, Board of Governors of the Federal Reserve System (U.S.).

IMF (2014): "World Economic Outlook" April 2014

Nakata, T., and S. Schmidt (2014): "Conservatism and Liquidity Traps," Finance and Economics Discussion Series 2014-105, Board of Governors of the Federal Reserve System (U.S.).

Nakov, A. (2008): "Optimal and Simple Monetary Policy Rules with Zero Floor on the Nominal Interest Rate," International Journal of Central Banking, 4(2), 73-127.

Reifschneider, D., and J. C. Williams (2000): "Three Lessons for Monetary Policy in a Low-Inflation Era," Journal of Money, Credit and Banking, 32(4), 936-966.

Please cite this note as:
Hills, Timothy, Taisuke Nakata, and Sebastian Schmidt (2016). "The Risk of Returning to the Effective Lower Bound: An Implication for Inflation Dynamics after Lift-Off," FEDS Notes. Washington: Board of Governors of the Federal Reserve System, February 12, http://dx.doi.org/10.17016/2380-7172.1690.