FRBSF ECONOMIC LETTER Number 2004-17, July 9, 2004 New Keynesian Models and Their Fit to the Data Central banks use macroeconomic models to help Hybrid New Keynesian models frame the issues that they face, to mold their ideas, Hybrid New Keynesian models have the canonical and to guide them in their decisionmaking.While model at their core, but they introduce a number a wide range of models are available, economists of important modifications.Typically these modi- are increasingly examining monetary policy issues fications seek to generate persistence in output and the design of optimal monetary policies in and inflation in order to slow down the rapid the context of “New Keynesian” macroeconomic adjustments that occur in the canonical model. models. New Keynesian models are notable for using microeconomic principles to describe the Consider, for a moment, the canonical model (see, behavior of households and firms, while allowing for example, Rotemberg and Woodford 1997). price and/or wage rigidities and inefficient market Households are assumed to smooth consumption outcomes. One particular model, often called the by saving or by borrowing against expected future canonical New Keynesian model, has received income; specifically, they save more when interest special attention, not only because it is easy to rates are high and consume more when interest work with, but also because it succinctly summa- rates are low. Firms are assumed to have some rizes the principal mechanisms through which market power, allowing those selling similar prod- policy interventions affect the economy. ucts to charge different prices. Although firms choose the price that they charge for their product, The canonical model does have some drawbacks, costs associated with changing prices—re-labeling however. For example, it arguably does an abysmal prices on goods, reprinting menus, etc.—hinder job of explaining movements in inflation, interest firms from changing prices frequently.As a result, rates, and output in the U.S. and elsewhere (Estrella a firm chooses today’s price based not only on and Fuhrer 2002).This poor empirical performance current demand for its product but also on the calls into question the value of the policy recom- price it expects to be able to sell its product mendations that emerge from it. Recognizing for tomorrow. this weakness, researchers have developed a new generation of models that retain the microeco- The problem with the canonical model is that the nomic approach to describing household and firm behavior of output, consumption, prices, and inter- behavior while also seeking to explain statistically est rates suggested by the model are fundamentally movements in observed data.These “hybrid” New at odds with observed data. Ball (1991) shows that Keynesian models, as they are known, are impor- the inflation equation in the canonical model implies tant because they are rapidly becoming the work- that a central bank can lower inflation to what- horse models in academic studies of monetary ever level it desires without any sacrifice in output policy.They are often used to construct a bench- or employment, let alone a recession.The reason mark for what constitutes optimal policy behavior, for this is that models with costly price adjustments to assess past policy decisions, to study the sources lead to persistence, or inertia, in prices, but not in and importance of macroeconomic disturbances, inflation (the rate of change in prices). Measured and to quantify the broad economic impact of inflation, however, is highly persistent, and the policy interventions. reduction in inflation that occurred in the early 1980s—commonly associated with tighter mon- In this Economic Letter, we discuss the basic proper- etary policy—was demonstrably not costless in ties of hybrid New Keynesian models and examine terms of output or employment: from July 1981 the extent to which they successfully explain U.S. to November 1982—the “Volcker recession”— macroeconomic data. over 2.8 million nonfarm payroll jobs were lost. FRBSF Economic Letter 2 Number 2004-17, July 9, 2004 Similarly,the canonical model suggests that consumers issues, the question arises whether they adequately can easily save or borrow against future income to describe the behavior of an economy like the U.S. smooth out fluctuations in current income. In con- Of course, because they invariably encompass the trast, studies typically find little evidence for con- canonical model, hybrid models will outperform sumption smoothing (see Hall 1988),finding the canonical model from an empirical standpoint, instead that a reduction in current income gener- but this does not imply that they necessarily fit the ally leads to a decline in consumption (Shea 1995). data well. Dennis (2003) develops and estimates a number of hybrid New Keynesian models and Hybrid New Keynesian models modify the canoni- assesses how well they describe the U.S. economy cal model by adding habit formation into consump- between 1982:Q1 and 2002:Q2. Figures 1 and 2 tion behavior. Roughly speaking, habit formation show the estimated responses of inflation and con- corresponds to the idea that households become sumption to a transitory supply shock—say,a short- accustomed to a certain standard of living and that lived oil price shock—using the hybrid model and they dislike having their consumption fall below a Vector AutoRegression (VAR).The VAR uses the that standard; but, if their consumption level does past history of the data to uncover statistical relation- drop, then they gradually become accustomed to ships among variables, restricting these relationships the lower living standard. Habit formation, in var- as little as possible, and, in particular, without impos- ious forms, has been used to explain survey results ing the New Keynesian theory on the data.The finding that people in rich countries appear to be VAR responses provide a benchmark for compar- no happier than people in poor countries, that some ing the hybrid New Keynesian model results.The people tend to be less concerned with their own shaded regions represent 95% confidence bands consumption than with what others consume, and around the VAR responses; in other words, accord- that some people tend to change their consump- ing to the VAR, only 5% of the time should we tion patterns gradually even after sudden large observe outcomes that lie outside these shaded increases in income. In terms of the hybrid model’s areas.With the VAR providing the benchmark, properties, habit formation leads to gradual changes occasions where the hybrid model’s responses lie in consumption over time because the standard outside the shaded regions indicate noteworthy of living that people become accustomed to depends departures from the benchmark behavior. on past consumption. To understand the figures, it is useful to interpret Increasingly, hybrid models also modify the canon- the responses from the hybrid model in terms of ical model by introducing indexation into firms’ the underlying theory.An adverse supply shock pricing decisions.The basic idea behind price pushes inflation up (Figure 1) causing the central indexation is that firms recognize that prices will bank to raise interest rates. Higher interest rates tend to rise over time, but they also find it costly induce consumers to defer consumption, causing to determine continuously the price they should consumption to fall (Figure 2). Facing lower demand charge for their goods. So, rather than reassess what for their product, firms gradually begin to lower price they should charge frequently, firms reassess their prices, and inflation begins to fall. As time their optimal price setting once a year (say) and passes, more and more firms lower their prices, and simply change their price according to observed indexing firms respond to falling inflation by also inflation on other occasions.While its theoretical lowering their prices.With inflation gradually falling, motivation is loose, the effect of price indexation the central bank is able to lower interest rates, which is to make inflation persistent.This persistence stimulates consumption spending.Through this arises because at any point in time some firms process, inflation and interest rates slowly decline, are simply changing their prices according to and consumption slowly rises, back to their pre- past inflation. vious levels.After about seven years (30 quarters) the shock has largely passed through the economy, With these modifications, the canonical model, having little further impact. which had no mechanism for generating persistence, is transformed into a framework in which both Looking at the responses from the hybrid model, households and firms make decisions based on past it is clear that habit formation and price indexation outcomes as well as on expected future outcomes. introduce considerable inertia into the model— shocks that last only one period lead to sustained Do hybrid models fit the data? movements in consumption and inflation.This Given that hybrid New Keynesian models are inertia represents the hybrid model’s contribution widely applied and are used to explore policy over and above the canonical model.Although the FRBSF Economic Letter 3 Number 2004-17, July 9, 2004 Figure 1 Conclusions Inflation responses to a supply shock Hybrid New Keynesian models are widely used Figure 1: Inflation responses to a supply shock to explore monetary policy issues and to identify Percentage points 1.20 and study the sources and importance of macro- VAR economic fluctuations.This Economic Letter has 1.00 95% confidence band discussed the economic behavior that underpins Hybrid model many hybrid New Keynesian models, described 0.80 how they improve on the canonical model, and examined their ability to replicate important char- 0.60 acteristics of U.S. data. By comparing the predic- tions of an estimated hybrid model to those from 0.40 a VAR, we found that the hybrid model generally performed well. However, the hybrid model strug- 0.20 gled to capture the economy’s response to supply shocks, suggesting that additional work is needed 0.00 to improve the model’s supply side and its rationale for why inflation is persistent.