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    STICKY INFORMATION VERSUS STICKY PRICES:A PROPOSAL TO REPLACE THE NEW

    KEYNESIAN PHILLIPS CURVE*

    N. GREGORY MANKIW AND RICARDO REISThis paper examines a model of dynamic price adjustment based on the

    assumption that information disseminates slowly throughout the population.Compared with the commonly used sticky-price model, this sticky-informationmodel displays three related properties that are more consistent with acceptedviews about the effects of monetary policy. First, disinflations are always contrac-tionary (although announced disinflations are less contractionary than surpriseones). Second, monetary policy shocks have their maximum impact on inflationwith a substantial delay. Third, the change in inflation is positively correlatedwith the level of economic activity.

    The dynamic effects of aggregate demand on output andinflation remain a theoretical puzzle for macroeconomists. Inrecent years, much of the literature on this topic has used a modelof time-contingent price adjustment. This model, often called "thenew Keynesian Phillips curve," builds on the work of Taylor[1980], Rotemberg [1982], and Calvo [1983]. As the recent surveyby Clarida, Gali, and Gertler [1999] illustrates, this model iswidely used in theoretical analysis of monetary policy. McCallum[1997] has called it "the closest thing there is to a standardspecification."Yet there is growing awareness that this model is hard tosquare with the facts. Ball [1994a] shows that the model yieldsthe surprising result that announced, credible disinflations causebooms rather than recessions. Fuhrer and Moore [1995] arguethat it cannot explain why inflation is so persistent. Mankiw[2001] notes that it has trouble explaining why shocks to mone-tary policy have a delayed and gradual effect on inflation. Theseproblems appear to arise from the same source: although theprice level is sticky in this model, the inflation rate can changequickly. By contrast, empirical analyses of the inflation process(e.g., Gordon [1997]) typically give a large role to "inflationinertia."

    * We are grateful to Alberto Alesina, Marios Angeletos, Laurence Ball, Wil-liam Dupor, Martin Eichenbaum, Christopher Foote, Xavier Gabaix, MarkGertler, Bennett McCallum, Kenneth Rogoff, Julio Rotemberg, Michael Woodford,and anonymous referees for comments on an earlier draft. Reis is grateful to theFundacao Ciencia e Tecnologia, Praxis XXI, for financial support.co 2002 by the President and Fellows of Harvard College and the Massachusetts Institute ofTechnology.The Quarterly Journal of Economics, November 2002

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    1296UA RT ERL Y JOURN A L OF EC ON OM IC SThis paper proposes a new model to explain the dynamic

    effects of aggregate demand on output and the price level. Theessence of the model is that information about macroeconomicconditions diffuses slowly through the population. This slow dif-fusion could arise because of either costs of acquiring informationor costs of reoptimization. In either case, although prices arealways changing, pricing decisions are not always based on cur-rent information. We call this a sticky -information model to con-trast it to the standard sticky-price model on which the newKeynesian Phillips curve is based.To formalize these ideas, we assume that each period afraction of the population updates itself on the current state of theeconomy and computes optimal prices based on that information.The rest of the population continues to set prices based on oldplans and outdated information. Thus, this model combines ele-ments of Calvo's [1983] model of random adjustment with ele-ments of Lucas' [1973] model of imperfect information.

    The implications of our sticky-information model, however,are closer to those of Fischer's [1977] contracting model. As in theFischer model, the current price level depends on expectations ofthe current price level formed far in the past. In the Fischermodel, those expectations matter because they are built intocontracts. In our model, they matter because some pricesetters are still setting prices based on old decisions and oldinformation.'After introducing the sticky-information model in Section I,we examine the dynamic response to monetary policy in SectionII. In contrast to the standard sticky-price model, which allowsfor the possibility of disinflationary booms, the sticky-informationmodel predicts that disinflations always cause recessions. Insome ways, the dynamic response in the sticky-information modelresembles Phillips curves with backward-looking expectations.

    1. We should also note several other intellectual antecedents. Gabaix andLaibson [2001] suggest that consumption behavior is better understood with theassumption that households update their optimal consumption only sporadically;it was in fact a presentation of the Gabaix-Laibson paper that started us workingon this project. Another related paper is Ball [2000], who tries to explain pricedynamics with the assumption that price setters use optimal univariate forecastsbut ignore other potentially relevant information. In addition, Rotemberg andWoodford [1997] assume a one-period decision lag for some price setters Finally,after developing our model, we became aware of Koenig [1997]; Koenig's model ofaggregate price dynamics is motivated very differently from ours and is applied toa different range of questions, but it has a formal structure that is similar to themodel explored here.

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    1298UA RT ERL Y JOURN A L OF EC ON OM IC Sever, but arrives randomly. Every period, a fraction X of firmsadjust prices. Each firm has the same probability of being one ofthe adjusting firms, regardless of how long it has been since itslast price adjustment.

    We start with three basic relationships. The first concernsthe firm's desired price, which is the price that would maximizeprofit at that moment in time. With all variables expressed inlogs, the desired price is

    *_Pt-ah.This equation says that a firm's desired price p* depends on theoverall price level p and output y. (Potential output is normalizedto zero here, so y should be interpreted as the output gap.) Afirm's desired relative price, p* p, rises in booms and falls inrecessions.

    Although we will not derive this equation from a firm's profitmaximization problem, one could easily do so, following Blan-chard and Kiyotaki [19871. Imagine a world populated by identi-cal monopolistically competitive firms. When the economy goesinto a boom, each firm experiences increased demand for itsproduct. Because marginal cost rises with higher levels of output,greater demand means that each firm would like to raise itsrelative price.

    In this model, however, firms rarely charge their desiredprices, because price adjustment is infrequent. When a firm hasthe opportunity to change its price, it sets its price equal to theaverage desired price until the next price adjustment. The ad-justment price x is determined by the second equation:

    x,=E1 -. J = 0

    According to this equation, the adjustment price equals aweighted average of the current and all future desired prices.Desired prices farther in the future are given less weight becausethe firm may experience another price adjustment between nowand that future date. This possibility makes that future desiredprice less relevant for the current pricing decision. The rate ofarrival for price adjustments, X, determines how fast the weightsdecline.

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    STICKY INFORMA TION V ERSUS STICKY PRICES299The third key equation in the model determines the overallprice level p:Pt =x E (1- x)Jxt_,.

    ,=0According to this equation, the price level is an average of allprices in the economy and, therefore, a weighted average of all theprices firms have set in the past. The rate of arrival for priceadjustments, X, also determines how fast these weights decline.The faster price adjustment occurs, the less relevant past pricingdecisions are for the current price level.

    Solving this model is a matter of straightforward algebra. Weobtain the following:

    at = [aX 2 /( 1X)]YtEt7rt+i,where iT t =pt pt _ i is the inflation rate. Thus, we obtain thenew Keynesian Phillips curve. Inflation today is a function ofoutput and inflation expected to prevail in the next period. Thismodel has become the workhorse for much recent research onmonetary policy.I.B. A Sticky -Information Model

    This subsection proposes an alternative model of price dy-namics. In this model, every firm sets its price every period, butfirms gather information and recompute optimal prices slowlyover time. In each period, a fraction X of firms obtains newinformation about the state of the economy and computes a newpath of optimal prices. Other firms continue to set prices based onold plans and outdated information. We make an assumptionabout information arrival that is analogous to the adjustmentassumption in the Calvo model: each firm has the same probabil-ity of being one of the firms updating their pricing plans, regard-less of how long it has been since its last update.

    As before, a firm's optimal price is_P t Pt ciY t-

    A firm that last updated its plans jperiods ago sets the pricext = ErrPr

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    1300UA RT ERL Y JOURN A L OF EC ON OM IC SThe aggregate price level is the average of the prices of all firmsin the economy:

    Pt = K E (1 - x ) i x ' , .j=0

    Putting these three equations together yields the following equa-tion for the price level:

    Pt = K E (1 - x).'Et-j(pt + ayt)J = 0

    The short-run Phillips curve is apparent in this equation: outputis positively associated with surprise movements in the pricelevel.

    With some tedious algebra, which we leave to the Appendix,this equation for the price level yields the following equation forthe inflation rate:

    ' r r t-Yt(1 - x)3Et_i_,(7rt + aAyt),xwhere Ay, = y, y,_ 1 is the growth rate of output. Inflationdepends on output, expectations of inflation, and expectations ofoutput growth. We call this the sticky-information Phillips curve.Take note of the timing of the expectations. In the standardsticky-price model, current expectations of future economic con-ditions play an important role in determining the inflation rate.In this sticky-information model, as in Fischer [1977], expecta-tions are again important, but the relevant expectations are pastexpectations of current economic conditions. This differenceyields large differences in the dynamic pattern of prices andoutput in response to monetary policy, as we see in the nextsection.

    One theoretical advantage of the sticky-information model isthat it survives the McCallum critique. McCallum [1998] hascriticized the standard sticky-price model on the grounds that itviolates a strict form of the natural rate hypothesis, according towhich "there is no inflation policyno money creation schemethat will keep output high permanently." Following Lucas [1972],McCallum argues that "it seems a priori implausible that a nation

    j=0

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    STICKY INFORMA TION V ERSUS STICKY PRICES301can enrich itself in real terms permanently by any type of mone-tary policy, by any path of paper money creation." The sticky-price model fails this test because a policy of permanently fallinginflation will keep output permanently high. By contrast, thesticky-information model satisfies this strict version of the natu-ral rate hypothesis. Absent surprises, it must be the case thatp, = Et_jpwhich in turn implies y, = O. Thus, the McCallumcritique favors the sticky-information Phillips curve over themore commonly used alternative.

    I I. IN F L A T I O N A N D O U T P U T D Y N A M I C S I N T H ES T ICK Y - INF O RMA T IO N MO D E L

    Having presented the sticky-information Phillips curve, wenow examine its dynamic properties. To do this, we need tocomplete the model with an equation for aggregate demand. Weuse the simplest specification possible:mP + Ywhere m is nominal GDP. This equation can be viewed as aquantity-theory approach to aggregate demand, where m is in-terpreted as the money supply and log velocity is assumed con-stant at zero. Alternatively, m can be viewed more broadly asincorporating the many other variables that shift aggregate de-mand. We take m to be exogenous. Our goal is to examine howoutput and inflation respond to changes in the path of m. 2

    As we proceed, it will be useful to compare the dynamics ofour proposed sticky-information Phillips curve with more famil-iar models. We use two such benchmarks. The first is the sticky-price model presented earlier, which yields the standard newKeynesian Phillips curve:

    1 Tt = 3YtEtiTt+1,where (3 = [aX2/(1 X)] and the expectations are assumed to beformed rationally. The second is a backward-looking model:

    ITt = 13Y7t -1.2. There are other, perhaps more realistic, ways to add aggregate demand tothis model. One possibility would be to add an IS equation together with aninterest-rate policy rule for the central bank Such an approach is more compli-cated and involves more free parameters. We believe the simpler approach takenhere best illustrates the key differences between the sticky-information model andmore conventional alternatives.

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    1302UA RT ERL Y JOURN A L OF EC ON OM IC SThis backward-looking model resembles the equations estimatedin the empirical literature on the Phillips curve (as discussed in,e.g., Gordon [1997]). It can be viewed as the sticky-pricemodel together with the assumption of adaptive expectations:Elr t+1 =1Tt- 1.When we present simulated results from these models, wetry to pick plausible parameter values. Some of these parametersdepend on the time interval. For concreteness, we take the periodin the model to equal one quarter. We set a = .1 and X = .25 (and,thus, (3 = .0083). This value of X means that firms on averagemake adjustments once a year. The small value of a means thata firm's desired relative price is not very sensitive to macroeco-nomic conditions. Note that the firm's desired nominal price cannow be written as

    13'; = (1 - a)p t + am t .If a is small, then each firm gives more weight to what other firmsare charging than to the level of aggregate demand.'

    We now consider three hypothetical policy experiments. Ineach experiment, we posit a path for aggregate demand m. Wethen derive the path for output and inflation generated by thesticky-information model and compare it with the paths gener-ated by the two benchmark models. The details of the solution arepresented in the Appendix. Here we discuss the dynamic pathsfollowed by output and inflation.ILA . Experiment 1: A Drop in the Level of A ggregate Demand

    The first experiment we consider is a sudden and permanentdrop in the level of aggregate demand. The demand variable m t isconstant and then, at time zero, unexpectedly falls by 10 percentand remains at this new level.

    The top graph in Figure I shows the path of output predictedby each of the three models. In all three models, the fall indemand causes a recession, which gradually dissipates over time.

    3. In the backward-looking model, the parameter 13 determines the cost ofdisinflation. According to this model, if output falls 1 percent below potential forone quarter, then the inflation rate falls by [3 if measured at a quarterly rate, or413 if annualized. If output falls by 1 percent below potential for one year, then theannualized inflation rate falls by 1613. Thus, the sacrifice ratiothe output lossassociated with reducing inflation by one percentage pointis 1/(16(3). Our pa-rameters put the sacrifice ratio at 7.5. For comparison, Okun's [1978] classic studyestimated the sacrifice ratio to be between 6 and 18 percent; Gordon [1997,footnote 8] puts it at 6.4. Thus, our backward-looking model is in the ballpark ofsimilar models used in the previous literature.

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    S T IC K Y IN FO R M A T IO N V E R S U S S T IC K Y PR I CE S303FI GUR E I

    Dynamic Paths after a 10 Percent Fall in the Level of Aggregate Demand at Time 0

    The impact of the fall in demand on output is close to zero atsixteen quarters. The backward-looking model generates an os-cillatory pattern, whereas the other two models yield monotonicpaths. Otherwise, the models seem to yield similar results.

    Differences among the models become more apparent, how-ever, when we examine the response of inflation in the bottom ofFigure I. In the sticky-price model, the greatest impact of the fall

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    1304UAR T ERL Y JOURN A L OF EC ON OM IC Sin demand on inflation occurs immediately. The other two modelsshow a more gradual response. In the sticky-information model,the maximum impact of the fall in demand on inflation occurs atseven quarters. Inflation could well be described as inertial.

    The inertial behavior of inflation in the sticky-informationmodel requires the parameter a to be less than one. Recall thatthe firm's desired price is

    0 = (1 a)pt + am t .If a = 1, then the desired price moves only with the money supply.In this case, firms adjust their prices immediately upon learningof the change in policy; as a result, inflation responds quickly(much as it does in the sticky-price model). By contrast, if a

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    S T IC K Y IN FO R M A T IO N V E R S U S S T IC K Y PR I CE S305FIGURE II

    Dynamic Paths Given an Unanticipated Fall in the Growth Rate of AggregateDemand at Date 0

    place, most price setters are still marking up prices based on olddecisions and outdated information. As a result of this inertialbehavior, inflation is little changed one or two quarters after thedisinflation has begun. With a constant money supply and risingprices, the economy experiences a recession, which reaches atrough six quarters after the policy change. Output then gradu-

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    1306UAR TERLY JOURNAL OF ECONOMICSally recovers and is almost back to normal after twenty quarters.These results seem roughly in line with what happens whennations experience disinflation.4ILC. Experiment 3: An Anticipated Disinflation

    Now suppose that the disinflation in our previous experimentis announced and credible two years (eight periods) in advance.Let us consider how this anticipated disinflation affects the pathof output and inflation.

    Figure III shows output and inflation according to the threemodels. The predictions for the backward-looking model are ex-actly the same as in Experiment 2: the assumption of adaptiveexpectations prevents the announcement from having any effect.But the results are different in the other two models, which positrational expectations.

    In the sticky-price model, the announced disinflation causesa boom. As Ball [1994a] emphasizes, inflation in this model movesin anticipation of demand. When price setters anticipate a slow-down in money growth, inflation falls immediately. This fall ininflation, together with continued increases in the money supply,leads to rising real money balances and higher output.

    By contrast, the sticky-information model does not producebooms in response to anticipated disinflations. In this model,there is no change in output or inflation until the disinflationarypolicy of slower money growth begins. Then, the disinflationcauses a recession.

    It would be wrong to conclude, however, that the announce-ment has no effect in the sticky-information model. Because of theannouncement, many price setters have already adjusted theirplans in response to the disinflationary policy when it begins. Asa result, an announced slowdown in money growth leads to aquicker inflation response and a smaller output loss than does asudden slowdown in money growth. For these parameters a dis-inflation announced and fully credible eight quarters in advancehas a cumulative cost that is about one-fifth the size of thesurprise disinflation.

    In a way, the sticky-information model combines elements of4. Ball [1994b1 examines disinflation for a number of countries. For the ninecountries for which quarterly data are available, he identifies 28 periods ofdisinflation. In 27 of these cases, the decline in inflation is associated with a fallin output below its trend level. This finding is related to the acceleration phenom-enon we document and discuss below.

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    1308UA RT ERL Y JOURN A L OF EC ON OM ICSIII. THE RESPONSE TO REALISTIC MONETARY SHOCKSSo far, we have compared how output and inflation respond

    to hypothetical paths for aggregate demand. We now take a steptoward greater realism. In particular, we assume a plausiblestochastic process for the money supply and then examine theimplied processes of output and inflation. As Christiano, Eichen-baum, and Evans [1999] discuss, economists have a good sense ofthe dynamic effects of monetary policy shocks. One way to gaugea model's empirical validity is to see whether it can generateplausible responses to such shocks.III.A . The Stochastic Process for the Money Supply

    We model the growth in the demand variable m as followinga first-order autoregressive process: Am t = p Am t _ i+ E t .In thisenvironment, the price level is nonstationary, but the inflationrate is stationary.

    To calibrate p, we looked at quarterly U. S. data from 1960 to1999. The variable m can be interpreted as a measure of moneysupply, such as M1 or M2, or more broadly as a measure ofaggregate demand, such as nominal GDP. The first autocorrela-tions for these time series are 0.57 for M1 growth, 0.63 for M2growth, and 0.32 for nominal GDP growth. Based on these num-bers, we set p = 0.5. The standard deviation of the residual is0.009 for Ml, 0.006 for M2, and 0.008 for nominal GDP, so weassume a standard deviation of 0.007 (although this choice affectsonly the scale and not the shape of the dynamic paths).

    The positive value of p means that a monetary shock buildsover time. That is, a positive shock Ecauses m to jump up andthen to continue to rise. With p = 0.5, the level of m eventuallyasymptotes to a plateau that is twice as high as the initial shock.This pattern for monetary shocks is broadly consistent with thatfound in empirical studies.5III.B. Impulse Responses

    Figure IV show the response of output and inflation to aone-standard-deviation contractionary monetary policy shock. Inall three models, output exhibits a hump-shaped response. Theimpact on output at first increases because demand is building

    5. For example, Christiano, Eichenbaum, and Evans [1998] conclude that anAR(1) process offers a good description of monetary policy shocks when using M2as the measure of money.

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    S T IC K Y IN FO R M A T IO N V E R S U S S T IC K Y PR I CE S309FI GU R E I V

    Dynamic Paths after a Negative One Standard Deviation (-0.007) Shockto the A R( 1 ) Aggregate Demand

    over time. It eventually decays because prices adjust. The back-ward-looking model yields oscillatory dynamics, whereas theother two models yield a monotonic recovery from the recession.

    The impulse responses for inflation to the monetary shockshow the differences between the sticky-price and sticky-informa-tion models. In the sticky-price model, inflation responds quickly

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    1310UAR T ERL Y JOURN A L OF EC ON OM IC Sto a monetary policy shock. In fact, the largest impact on inflationoccurs immediately. By contrast, the sticky-information modeldisplays some of the inflation inertia that is built into the back-ward-looking model. For these parameters, a monetary policyshock in the sticky-information model has its maximum impacton inflation after seven quarters.

    The impulse response function for the sticky-information modelis far more consistent with conventional views about the effects ofmonetary policy. Economists such as Friedman [1948] have empha-sized the long lags inherent in macroeconomic policy. In particular,a long lag between monetary policy actions and inflation is acceptedby most central bankers and confirmed by most econometric stud-ies.6 Figure IV shows that the sticky-information model can explaina long lag between monetary policy shocks and inflation, whereasthe standard sticky-price model cannot.III. C. Inflation Persistence

    Fuhrer and Moore [1995] argue that the standard sticky-price model "is incapable of imparting the persistence to inflationthat we find in the data" [p. 127]. In the model, they claim, "theautocorrelation function of inflation . . . will die out very rapidly"[p. 152]. This contradicts the empirical autocorrelations of infla-tion, which decay slowly.

    Motivated by these arguments, we calculated the impliedautocorrelations of inflation in our three models. We maintain theempirically realistic process for money growth used above: A m t =0.56nt_ 1 + E t . Table I presents the first eight autocorrelations ofinflation implied by the models, as well as the actual autocorre-lations of inflation using the GDP deflator, the consumer priceindex, and the core CPI. (The core CPI is the index excluding foodand energy.) Notice that inflation is highly autocorrelated in allthree models. That is, given the empirically realistic process forthe money supply, all the models deliver plausible persistence ininflation.

    In the end, we agree with Taylor [1999, p. 1040], who re-sponds to Fuhrer and Moore by observing that "inflation persis-tence could be due to serial correlation of money." This is why allthree models deliver high autocorrelations in Table I. Yet we alsoagree with Fuhrer and Moore's deeper point: the standard sticky-

    6. See, for example, Bernanke and Gertler [1995] or Christiano, Eichenbaum,and Evans [1999].

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    STICKY INFORMA TION V ERSUS STICKY PRICES311TABLE IA U T O C O R R E L A T I O N S F O R I N F L A TI O N : P R E D I C TE D A N D A C T U A LSticky-informationmodel

    Sticky-pricemodel

    Backward-lookingmodel

    Actual:GDPdeflator

    Actual:CPI

    Actual:coreCPI

    1 0.99 0.92 0.99 0.89 0.76 0.762 0.95 0.85 0.98 0.83 0.72 0.713 0.89 0.78 0.96 0.81 0.73 0.694 0.82 0.71 0.94 0.78 0.62 0.595 0.74 0.65 0.90 0.71 0.57 0.556 0.66 0.59 0.86 0.65 0.51 0.547 0.57 0.54 0.81 0.61 0.44 0.468 0.48 0.50 0.75 0.58 0.33 0.38

    The first three columns of this table show the autocorrelations of inflation predicted by three models.These calculations assume that money growth follows the process Am t = 0.5 Am + E.The modelparameters are set to o = .1 and X = .25. The last three columns show the actual autocorrelations of quarterlyinflation rates.

    price model does not deliver empirically reasonable dynamics forinflation and output. The key empirical fact that is hard to match,however, is not the high autocorrelations of inflation, but thedelayed response of inflation to monetary policy shocks.'

    IV. THE ACCELERATION PHENOMENONWhen economists want to document the Phillips curve rela-

    tionship in U. S. data from the last few decades of the twentiethcentury, a common approach is to look at a scatterplot of thechange in inflation and some level of economic activity, such asunemployment or detrended output. This scatterplot shows thatwhen economic activity is vigorous, as represented by low unem-ployment or high output, inflation tends to rise. We call thiscorrelation the acceleration phenomenon.'

    Panel A of Table II demonstrates the acceleration phenome-non using U. S. quarterly data from 1960 to 1999. For these

    7. Fuhrer and Moore also emphasize the persistence of inflation in responseto "inflation shocks," which could be interpreted as supply shocks. The model wehave developed here cannot address this issue, because there are no supplyshocks. In Mankiw and Reis [2001] we take a step toward remedying thisomission.8. For some examples of economists using such a scatterplot to demonstratethe acceleration phenomenon, see Abel and Bernanke [1998, p. 4571, Blanchard[2000, p. 155], Dornbusch, Fischer and Startz [2001, p. 1091, Hall and Taylor[1993, p. 2171, and Stock and Watson [1999, p. 48].

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    1312UA RT ERL Y JOURN A L OF EC ON OM ICSTABLE II

    THE ACCELERATION PHENOMENON

    COST (.Yt/iTt+2r t 2) COST (YtOrt+4Tt-4)A . ActualGDP deflator .4 8 .6 0CPI .3 8 .4 6Core CPI .4 6 .51B. Predicted

    Backward-looking model .9 9 .9 9Sticky-price model .13 .11Sticky-information model .4 3 .4 0

    Panel A shows the correlation between output and the change in inflation in U. S. quarterly data from1960 to 1999. The variable y is measured as log real GDP detrended with the Hodrick-Prescott filter. PanelB shows the correlation between output and the change in inflation predicted by three models. Thesecorrelations assume that money growth follows the process: Am, = 0.5 Am, 1 + Et. The model parametersare set to a = .1 and X = .25.

    calculations, output yt is the deviation of log real GDP from trend,where trend is calculated using the Hodrick-Prescott filter. Weuse three measures of inflation: the GDP deflator, the CPI, andthe core CPI. We use two timing conventions: we correlate yt withirt+2he one-year change in inflation centered aroundthe observation date, and with Trt4 T r t- 4 , the two-year changein inflation. All sixcorrelations are positive and statisticallysignificant. In U. S. data, high output is associated with risinginflation.

    We now consider whether the models can generate the posi-tive correlation between output and the change in inflation. Weassume the same stochastic process for the money supply as inthe previous section (A m t = . 56 nt-1+ E t) and the sameparameters (a = .1 and X = .25). Then, as explained in theAppendix, we compute the population correlation between outputand the change in inflation.

    Panel B of Table II shows the correlation predicted by themodels. Not surprisingly, the backward-looking model predicts ahigh correlation. Because 7r, - Trt _ i= Pyt in this model, thecorrelation is perfect for the one-period change in inflation andonly slightly lower for longer changes. In essence, the modelbuilds in the acceleration phenomenon through the assumption ofadaptive expectations. This is hardly a major intellectual victory:the appeal of the backward-looking model comes not from itstheoretical underpinnings but fromits ability to fit thisphenomenon.

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    S T IC K Y IN FO R M A T IO N V E R S U S S T IC K Y PR I CE STABLE III

    THE ACCELERATION PHENOMENON: SENSITIVITY ANALYSIS

    1313

    A . Sticky-price modela = .05 a = .1 a = .5 a= 1.0X = .10.08 -0.09 -0.12 -0.13X = .250.12 -0.13 -0.15 -0.15X = .50.15 -0.15 -0.13 -0.11B. Sticky-information model a = .1 a = .5 a = 1.0= .05X = .1.49 0.39 0.05 -0.04X = .25.51 0.43 0.12 0.02X = .5.52 0.44 0.21 0.13

    This table shows the correlation between output y, and the change in inflation arr t+2 -hesecorrelations assume money growth follows the process: Am =0.5 + Et.We next look at the two models with better foundations.Table II shows that the sticky-price model yields no associationbetween output and the change in inflation. For the one-yearchange, the correlation between these variables is -0.13, which issmall and the wrong sign. By contrast, the sticky-informationmodel yields a strong, positive association. According to thismodel, the correlation between output and the change in inflationis 0.43.9

    To understand these results, recall the impulse response func-tions. In the sticky-price model, when the economy experiences acontractionary monetary shock, output falls for a while. Inflationfalls immediately, and then starts rising. Thus, low output coincideswith falling inflation at first, but then coincides with rising inflationfor a long period. This generates the small, negative correlation.By contrast, in the sticky-information model, inflation ad-justs slowly to a monetary shock. When a contractionary shocklowers output, it also leads to a prolonged period of falling infla-tion. This generates the positive correlation between output andthe change in inflation.

    Table III presents a sensitivity analysis of this correlation toalternative parameter values. Panel A of the table shows the9. Our finding that the calibrated sticky-price model predicts a negativecorrelation between y and Dar (in contrast to the positive correlation in the data)is related to Gali and Gertler's finding [1999] that econometric estimation of thismodel yields a coefficient on output of the wrong sign. Gali and Gertler's proposedfix to the sticky-price model, however, differs substantially from the sticky-information model proposed here.

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    1314UA RT ERL Y JOURN A L OF EC ON OM IC Scorrelation produced by the sticky-price model for different pa-rameter values. Panel B shows the correlation produced by thesticky-information model. The sticky-price model consistentlygenerates a small correlation of the wrong sign, whereas thesticky-information model typically yields a positive correlationbetween output and the change in inflation. 1

    V. RESPONSES TO SK EPTICSA skeptic of the sticky-information model might naturally

    ask two questions. What is the evidence for the model? What arethe model's microeconomic foundations? At this point, we cannotgive definitive answers, but we can offer some suggestive insights.V.A. Evidence

    We were motivated to explore the sticky-information modelby a set of empirical anomalies. As we have discussed, the canoni-cal sticky-price model of inflation-output dynamics cannot bereconciled with the conventional wisdom about the effects ofmonetary policy, whereas the sticky-information model is consis-tent with the conventional wisdom. This fact is itself evidence infavor of this model compared with the leading alternative.

    Our skeptic might say that the backward-looking model, withits assumption of adaptive expectations, can also be reconciled withthe conventional wisdom. Or he might claim that the sticky-infor-mation model is little more than a revival of adaptive expectations.There are, however, at least two key differences between the sticky-information model and the backward-looking model, and they arguein favor of the sticky-information model. Both of these differencesarise from the fact that agents in the sticky-information model formexpectations rationally, even though they do not do so often.

    One difference relates to changes in regime. As Barsky [1987]and Ball [2000] point out, inflation has been close to a randomwalk in the period since World War II, whereas before World WarI, when the gold standard was in effect, it was close to white noise.The sticky-information model predicts that the reduced-form

    10. These simulated correlations are computed under the assumption that allfluctuations are due to demand shocks. If we were to append supply shocks to thismodel, the predicted correlations would likely be driven down, because suchshocks push inflation and output in opposite directions. Thus, supply shockswould make it even harder for the sticky-price model to match the positivecorrelation in the data.

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    S T IC K Y IN FO R M A T IO N V E R S U S S T IC K Y PR I CE S315Phillips curve should shift in response to this regime change. Inthe recent period, expected inflation should roughly equal pastinflation, and output should be related to changes in inflation;that is, the data should conform with the accelerationist Phillipscurve. In the early period, expected inflation should be roughlyconstant, and output should be related to the level of inflation;that is, the data should conform with the classic Phillips curve.Ball [2000] reports that these two predictions hold true in thedata, which is inconsistent with the backward-looking modelstrictly construed as a structural relationship.'

    A second difference between the sticky-information modeland the backward-looking model concerns the role of credibility.In the model with backward-looking expectations, credibility inmonetary policy has no role. By contrast, in the sticky-informa-tion model, credibility can reduce the costs of disinflation. Mostcentral bankers believe that credibility is important, but thisbelief is hard to confirm empirically. One intriguing study is thatof Boschen and Weise [2001], which examines 72 disinflationaryepisodes from 19 OECD countries. This study measures credibil-ity as the probability of success conditional on economic andpolitical variables known at the start of the disinflation. Theyreport that credibility lowers the output cost of reducing inflation.This finding is consistent with the sticky-information model butnot with the backward-looking model.Our skeptic might also ask for evidence on whether pricesetters actually respond to information slowly. One piece of evi-dence comes from Zbaracki et al. [2000], a study of the costsassociated with changing prices at a large manufacturing firm. Inthis extensive case study, the authors find that only a smallpercentage of these costs are the physical costs of printing anddistributing price lists. Far more important are the "managerialand customer costs," which include the costs of information-gathering, decision-making, negotiation, and communication.Whether our sticky-information model captures the effects ofsuch costs is an open question, but this microeconomic evidencesuggest that macroeconomists need to think broadly about thefrictions that impede price adjustment.

    11. Although the sticky-information model is consistent with Ball's findings,other models may be as well. Ball proposes his own explanation: agents areassumed to follow optimal univariate forecasts but to ignore information in othervariables. In Ball's theory, the optimal univariate forecasting rule changes whenthe monetary regime changes.

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    1316UA RT ERL Y JOURN A L OF EC ON OM IC SIn a recent paper Carroll [2001] reports some direct evidence

    on the slow dissemination of information about inflation. Moti-vated in part by our sticky-information model, Carroll comparesthe inflation expectations from surveys of two groups: profes-sional forecasters and the general public. Not surprisingly, hefinds that the professional forecasters are better at forecastinginflation than the general public is. More important, he finds thatthe general public's expectations respond to the professionals'expectations with a lag. Based on the assumption that profession-als do not suffer from sticky information, he estimates a parame-ter similar to our X that measures how quickly the public's ex-pectations catch up. Remarkably, the estimated value of X isalmost exactly the 0.25 that we assumed above. 12

    Carroll [2001] also reports two related pieces of evidence thatcannot be explained with the sticky-information model as pre-sented here. He finds that the professional's and the public'sexpectations are closer on average when there are more newsstories about inflation. In addition, when there are more newsstories about inflation, the public's expectations adjust more rap-idly to the professional's expectations. Thus, although Carroll'sstudy is consistent with the hypothesis that the public's inflationexpectations adjust slowly, it suggests that the rate of informa-tion acquisition X is not constant over time.V.B. Microfoundations

    The starting point of this paper is the premise that some pricesetters respond to information about monetary policy with a lag.This hypothesis raises many questions. Why, exactly, do people setprices based on outdated information? What set of constraints on theprocess of decision-making leads to this outcome? How can econo-mists model these imperfections in human understanding?

    One approach to answering these questions is to use the toolsof information theory, as exposited, for instance, in the textbookby Cover and Thomas [1991]. Drawing on these tools, Sims [2001]suggests modeling humans as having a limited channel for ab-sorbing information. Woodford [2001] uses this idea to build amodel of inflation-output dynamics In his model, because pricesetters learn about monetary policy through a limited-informa-tion channel, it is as if they observe monetary policy with a

    12. In Mankiw and Reis [2001] we econometrically implement a model closelyrelated to the one developed here. We also find that X = 0.25 fits the data well.

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    S T IC K Y IN FO R M A T IO N V E R S U S S T IC K Y PR I CE S317random error and have to solve a signal-extraction problem alongthe lines of Lucas [1973].As Woodford [2001] notes, his noisy-information model is pro-posed in the same spirit as the sticky-information model explored in

    this paper. The difference between the models is how informationarrives. In Woodford's model, price setters get a noisy signal aboutmonetary policy in every period. In our model, price setters obtainperfect information about monetary policy with probability X inevery period. This difference in information arrival leads to somedifferences in the dynamic response to monetary policy. 13

    Information theory, however, may not be the best approach tomicrofoundations. For most people, it is easy to find out what themonetary authority is doing, but it is much harder to figure out whatit means. As Begg and Imperato [2001] emphasize, the real cost isthe cost of thinking One interpretation of the sticky-informationmodel is that because thinking is costly, people do it only once in awhile and, at other times, continue with outdated plans.

    At best, this time-contingent approach to thinking is only anapproximation. How much a person thinks about an issue de-pends on the benefit of doing so. Most people spend little timethinking about monetary policy, but circumstances can affect theallocation of their mental resources. This might explain Carroll'sfinding that the public's expectations of inflation adjust morerapidly when there are more news stories about inflation. Simi-larly, the ends of hyperinflations (as studied by Sargent [1982])may be different than more typical disinflations (as studied byBall [199413]) because the major institutional reforms that endhyperinflations are exceptionally newsworthy events.

    In the end, microfoundations for the Phillips curve may re-quire a better understanding of bounded rationality. But untilthose foundations are established, the sticky-information modelas described here may offer a useful tool for the study of inflation-output dynamics.

    VI . C O NC L USI O NThis paper has explored a dynamic model of price adjust-

    ment. In particular, we have proposed a model to replace the13. Our model, like Woodford's, starts by simply assuming the nature of theinformation flow. Alternatively, one could start by assuming some cost of using aninformation channel and then derive the optimal flow of information. See Mosca-rini [2001] for an exploration of this issue in a different context.

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    1318UA RT ERL Y JOURN A L OF EC ON OM IC Swidely used "new Keynesian Phillips curve." In this model, pricesare always changing, but decision-makers are slow to updatetheir pricing strategies in response to new information.

    Although the choice between the sticky-information modeland the standard sticky-price model is ultimately an empiricalissue, three of our findings suggest that the sticky-informationmodel is more consistent with accepted views of how monetarypolicy works. First, in the sticky-information model, disinfla-tions are always contractionary (although announced disinfla-tions are less costly than surprise ones). Second, in the sticky-information model, monetary shocks have their maximumeffect on inflation with a substantial delay. Third, the sticky-information model can explain the acceleration phenomenonthat vigorous economic activity is positively correlated withrising inflation.

    The dynamic patterns implied by the sticky-informationmodel resemble those from the Fischer [1977] contracting model,although long-term contracts have no role. In both models, pastexpectations of the current price level play a central role ininflation dynamics In a sense, the slow dissemination of infor-mation in our model yields a nominal rigidity similar to the oneFischer assumed in his contracts.Critics of the Fischer contracting model (e.g., Barro [1977])have noted that it is hard to rationalize signing such contracts exante or enforcing them ex post in light of the obvious inefficienciesthey cause. Such critiques do not apply to the model proposedhere. The assumption of slow information diffusion, perhaps dueto costs of acquiring or acting on new information, leaves noapparent, unrealized gains from trade. Thus, sticky informationoffers a more compelling rationale for this type of nominal rigidity.

    Moving the theory of price adjustment away from stickyprices toward sticky information may seem like a radical sugges-tion, but we temper it with an important observation: manylessons from the "new Keynesian" literature on price adjustmentapply as well to our sticky-information model as they do to thestandard sticky-price model.

    An early lesson about price adjustment by firms with somedegree of monopoly power is that the private losses from stickyprices are only second order, even if the social losses are firstorder [Mankiw 1985; Akerlof and Yellen 1985]. Thus, if firms facesmall costs of price adjustment or are only near rational, theymay choose to maintain sticky prices, even if the macroeconomic

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    S T IC K Y IN FO R M A T IO N V E R S U S S T IC K Y PR I CE S319effect of doing so is significant. When we move from sticky pricesto sticky information, this lesson applies in somewhat modifiedform. If there are small costs of acquiring information or recom-puting optimal plans, firms may choose not to update their pric-ing strategies. The private loss from maintaining old decisions,like the cost of maintaining old prices, is second order.

    Another lesson from the literature on price adjustment isthat real rigidities amplify monetary nonneutralities [Ball andRomer 1990]. Real rigidity is defined as a lack of sensitivity ofdesired relative prices to macroeconomic conditions. Here, thistranslates into a small value of the parameter a. Real rigiditiesalso play a role in our sticky-information model. Price setters whoare updating their decisions are aware that other price setters arenot, and this knowledge limits the size of their adjustments,especially when a is small. As a result, real rigidity tends toexacerbate the effects of monetary policy.

    An advantage of sticky-information over sticky-price mod-els is that they more naturally justify the widely assumedtime-contingent adjustment process. If firms have sticky pricesbecause of menu costs but are always collecting informationand optimizing in response to that information, then it isnatural to assume state-contingent adjustment. Dynamic mod-els of state-contingent adjustment, however, often yield empir-ically implausible results; Caplin and Spulber's [1987] conclu-sion of monetary neutrality is a famous example. By contrast,if firms face costs of collecting information and choosing opti-mal plans, then it is more natural to assume that their adjust-ment process is time-contingent. Price setters cannot reactbetween scheduled adjustments, because they are not collect-ing the information and performing the calculations necessaryfor that purpose.

    Yet we must admit that information processing is more com-plex than the time-contingent adjustment assumed here. Modelsof bounded rationality are notoriously difficult, but it seems clearthat when circumstances change in large and obvious ways, peo-ple alter the mental resources they devote to learning and think-ing about the new aspects of the world. Developing better modelsof how quickly people incorporate information about monetarypolicy into their plans, and why their response is faster at sometimes than at others, may prove a fruitful avenue for futureresearch on inflation-output dynamics.

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    1320UA RT ERL Y JOURN A L OF EC ON OM ICSA P P E N D I X : D E T A I L S O F S O L U T I O N S

    This Appendix explains the solutions of the three modelspresented in the text.A. The Derivation of the Sticky - Price Phillips Curve

    From the equations for the adjustment price x t and the pricelevel pt , breaking the sum and using the law of iterated expecta-tions, we obtain(Al)t = X/3-k (1 (A2)t = Xxt+ ( 1 X ) P t - i But then solving for xt in (A2) and replacing in (Al) for x t andxt1, together with the definition of pt = p t + aye , yields thedesired expression for inflation presented in the text.B. The Derivation of the Sticky - Information Phillips Curve

    Begin with the equation for the price level derived in the text:

    (A3)t =x E (1 x)3Et-,(pt + etyt),=0By taking out the first term and redefining the summation index,this equation can be written as

    (A4) Pt = X(Pt + ayt) + A E (1 aye).j= 0Analogous to equation (A3), the previous period's price level canbe written as(A5) Pt 1 =X E (1 ayt_D,=0Subtracting (A5) from (A4) and rearranging yields the followingequation for the inflation rate:

    Trt= X(Pt+ otYt) + X E1 xotAyi)= 0(A6) x 2 E1 x)JEt_i-,(Pt + an).J=0 atUniversityofWarwickonFebruary1,2012http://qje.oxfordjournals.org/Downloadedfrom

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    S T IC K Y IN FO R M A T IO N V E R S U S S T IC K Y PR I CE S321Now equation (A4) can be rearranged to show that(A7) P 1 _lYt = X E (1 x)'Et-i-j(Pt + elyt)j= 0We now use equation (A7) to substitute for the last term inequation (A6). After rearranging, we obtain

    (A8) art = r aX[1_ x jYx E ( 1 rt + o t A . Y t ) J= 0This is the sticky-information Phillips curve presented in the text.C. The Response of Output and Inflation in the Policy

    ExperimentsThe three policy experiments we undertake can be described

    as follows:(El) An unexpected fall in the level of aggregate demand by

    10 percent at date O. Thus, m t = log (0.9) for t 0),generating the oscillatory behavior.

    For the sticky-price model, rewrite the Phillips curve, usingthe aggregate demand equation, as( A 1 0 ) EtPt+i ( 2 + R)Pt + Pt-i = R m t .This is an expectational difference equation, which can be solvedby the methods explained in Sargent [1987]. First, take expecta-tions at tand express all expectations at t variables with anasterisk. Then using the lag operator L, such that LE tpt =

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    1322UAR TERLY JOURNAL OF ECONOMICSEtpt _ l and its inverse, the forward operator, F = L -1 such thatFE tpt = Etpt,i , reexpress (A10) as(All)F2 (2 + (3)F + 1)Lp =The quadratic (x2 (2 + (3)x + 1), has two positive roots: 0 and1/0, such that (1 0)2/0 = p. Pick 0 to correspond to the smallerof the roots. Then (All) becomes(Al2)1 (1 0) 2 (1 F0) -1m 1 '.But using the fact that 0 < 1, the inverse on the right-hand sideis well defined and can be expanded. Finally, because pt and pt _ lare part of date t information set, we obtain the final solution:

    ( A 1 3 ) Pt = OPt-i + ( 1 0) 2 E ORtmt+,i = oFor the policy experiment El, up to date 0, pt = m t =log

    (0.9). From 0 onwards, Etm t+ , = m t+, =0, so the price level isgiven by the recursion pt = Op t- 1 with initial condition ;3_ 1 =log (0.9). For E2, pt = mt until t = 1, and after again pt =Op t _ i, but now the initial condition isp=0. Thus, pt =0, t0, and so yt = 0 at all t. For E3, in the period 8t1, thenthe terms of the sum in the right-hand side of (A13) are Etm t+, =0.025(1 + t) for 8 t +i1 and Etmt, =0 for t +0. After that, for t, pt = Opt-i.Finally, consider the sticky-information model, as capturedby the equation:

    ( A 1 4 ) Pt = X E (1 - x)JEt_,[(1- Opt+ unlitj=0

    The price level at time tcan then be broken into twocomponents, where the first includes price setters aware of thenew path for aggregate demand, and the second those agents whodecided on their prices before the change:

    (A 15) Pt = X E (1 - x).Et_a)Pt + cunt]j=0+ X E (1 - x)'Et_.,[(1 - a)Pt + amt].

    j=t+1

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    S T IC K Y IN FO R M A T IO N V E R S U S S T IC K Y PR I CE S323Because the agents represented by the second term are stillsetting prices based on their old information sets, their expecta-tions are given by E t _fpt = Et _im t =log (0.9). As a result, thesecond term reduces to log (0.9) (1 X)'. The agents repre-sented by the first term have responded to the new path ofaggregate demand, so E t _im, = 0, and because there is nofurther uncertainty, E t _jp t = pt . Collecting terms and rearrang-ing, we obtain the solution:( A 1 6 ) Pt = [log (0.9)(1 X)']/[1 (1 14(1 (1 X)')].This equation gives the solution for the price level in the sticky-information model under policy experiment El.We can find the outcome under policy experiment E2 withsimilar steps. Under E2, however, Et t= Et _jm t = 0.025(1 +t) for t j< O. Thus, the solution is( A 1 7 ) Pt =[0.025(1 + t)(1 X)']/[1 (1 a)(1 (1 X)')].This equation gives the price level in the sticky-informationmodel under policy experiment E2.

    Finally, for E3, for t < 0, the path is the same as expected byall agents, so p, = m t =0.025(t + 1) and y, =O. After date 0,p, is given by (note the limit of the sums)

    t+8( A 1 8 ) Pt =X E (1 - X)/Et-,[(1- a)Pt + ant]j= o

    + X E (1 - x)'.E,_,[(1- a)p t + am t].j=t+9

    All else is the same as in E2. The solution follows as(A19) Pt =[0.025(1 + t)(1 X)']/[1 (1 a)(1 (1 X)')].This equation gives the path of the price level for the sticky-information model under policy experiment E3.D. Output and Inflation When Money Growth Is A R(1)

    Suppose that Am, = pAmt _ i+ E t,where Et is white noiseand Ipl < 1. It will prove convenient to write this in M A (so) form:C O.

    (A20)mt = E p iE t_ior m=E E pj,_;_ k j=0=0 j=0 atUniversityofWarwickonFebruary1,2012http://qje.oxfordjournals.org/Downloadedfrom

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    1324UA RT ERL Y JOURN A L OF EC ON OM ICSConsider first the backward-looking model. First-differenc-

    ing both sides of (A9), multiplying through by (1 pL) andrearranging yields the following AR(3) for the inflation rate:(A21)= [1 + 13]-12+PhT-i

    (2p + 1) , T r t _ 2 + pir t _ 3 + 130.From this equation we can calculate impulse responses and allmoments of inflation.

    Consider now the sticky-price model. We find the generalsolution of these rational expectation models by the method ofundetermined coefficients as outlined in Taylor [1985]. Becausethe money growth rate is stationary, it is a reasonable conjecturethat the inflation rate is also stationary and so can be expressedin the MA(00) general form:

    (A22)Er PtE E (t);Et_i_k,==0 j=0where the (1) .7 are coefficients to be determined Then realize thatE t [E ti _j_ k } = E t+,_j_ k for i j knd is zero otherwise. Usingthe solution of the model in (A13),

    CO000(A23)E E () -j-k =0 E E 43JEt 1 kk=0 j=0=0 j=0

    + (1 0) 2 E et E+,-,-k,= 0=0 k=max {i-j,0}But then, because this must hold for all possible realizations ofE t matching coefficients on both sides of this equation yields forthe coefficient on E t : 1 0(i)c, = (1 0) 2 E 0i E P = 1 Op And for a general v, the coefficient on s t _ v :

    v-1-Ev(A25)4;= 0 E + ( 1 0) 2 E 0i E P i.j=0=0=0=0(A24) i=0=0 atUniversityofWarwickonFebruary1,2012http://qje.oxfordjournals.org/Downloadedfrom

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    S T IC K Y IN FO R M A T IO N V E R S U S S T IC K Y PR I CE S325This yields[ 1pv+(A26) (1),,_ (0 - 1) E(1 - 0) 2 ]1 _ p Op] J = o

    Equations (A22), (A24), and (A26) fully describe the stochasticprocess of inflation. The impulse response of inflation for a unitshock to aggregate demand is given by {kJ. The autocorrelationcoefficients of orderjare then given by (see Hamilton [1994],p. 52)

    (A27) E() v=j=0Consider now the sticky-information model. Similarly to(A22), conjecture the solution: ar t E -yiE t _, orpt = - - "Yzt-z-k,where the sums go from 0 to infinity Taking the relevant expec-

    tations and substituting in (A8), the equation for the Phillipscurve, we obtain(A28)

    00Ei=0 =

    CX D0ctx E Ex il i=0=0 COEi=0 CCE Etkik =0P iEtki+ x Ex ) ia)E - yi E t _ i+a

    j= 0=j+i=j+1So, again matching coefficients,

    'Yo = aX/[1 - X(1 -

    .yk = ax 1- x(i - 0 aE - Yk- 1[x, y iEi + pk E - x y l.

    This provides the full characterization of the stochastic processfor inflation. Impulse responses, autocorrelations, and cross cor-relations can be easily calculated.

    (A29)

    (A30)0

    k-1i = 0=1=1 atUniversityofWarwickonFebruary1,2012http://qje.oxfordjournals.org/

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  • 8/3/2019 Mankiw - Sticky Information Versus Sticky Prices

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    1326UARTERLY JOURNAL OF ECONOMICSE. Impulse Responses of Output and Population Correlations

    between Output and the Change in InflationFor the backward-looking model, corr (ir t+2Tt-2/ Y t)c o rr [ i T t + 2Tt-2/ ( 1T tTt--1)/13] which we can evaluate using(A21). Corr ( IT t+4t-4, Yt) follows likewise.For the sticky-price model, note that output growth is givenfrom the quantity theory: Ay, = Am, - art =E (p" -From this, we can obtain the MA(co) for output: y, = wi,_iwiththe recursion o = 0) 7 _ 1 + p3 - 4:1: n / , initiated by coo = 1 - 40. Theimpulse response to a unit shock is given by the sequence {co y }. Tosolve for the change in inflation 7r, - 7r,_ 4, start with 7r, = E

    4 )j,-j; the coefficients in the MA(00) representation for the changein inflation 7r, - art-4 = Ere then given by ti= 4 - (130j_4with to =4/0) 1 = 41) S 2 = 412, and t3 = 413. Given these results,the population cross correlation between the change in inflationand output, corr

    (A31)()Av +2v =0v =0= 0The cross-correlation corr ( iTt+ 4 Irt-4,Yt) is derived in the samefashion.The derivation of the population cross correlations in thesticky-information model is precisely the same, except we startwith 7r, =-y,E t_ i as the process for inflation.DE