Evaluating Monetary Policy Rules in Estimated Forward-Looking Models: A Comparison of US and German Monetary Policies.

In this paper, we estimate two small, forward-looking, macroeconomic models for the US and Germany and we compare the implied optimal monetary policy rules. Both models have a standard structure: an I-S curve, a Phillips curve, a short term interest-rate rule and a long term interest rate determined by the Expectations Hypothesis. They are intended to fit the data while allowing for some forward-looking behavior. They are estimated from 1968 to 1998, using the full-information maximum-likelihood procedure, so that forward-looking expectations are fully model-consistent. In order to evaluate monetary policy, we compute optimal policy frontiers and we perform some simulations of the model. German optimal monetary policy is found to require a more persistent and slightly stronger response to inflation and output than the US optimal policy.Forward-looking model ; monetary policy rules

ML vs GMM Estimates of Hybrid Macroeconomic Models (With an Application to the New Phillips Curve)

Many macroeconomic models involve hybrid equations, in which some variables are a function of both their lags and their expected future value. The hybrid "New Keynesian" Phillips Curve is a prominent example. Estimates of such hybrid models have produced conflicting empirical results: Studies which use ML estimation tend to find the forward-looking component to be small, while those using GMM have reported the inflation dynamics to be predominantly forward-looking. This paper provides a rationalization for this empirical conflict. Allowing for two alternative and straightforward mis-specifications (measurement error and omitted dynamics) in a hybrid model, we show that the ML estimator tends to undervalue the weight of the forward-looking component, while the GMM estimator tends to overstate it. This result is shown to hold analytically in a simple DGP. Monte-Carlo experiments indicate that it remains valid in a wide range of more plausible DGPs. Simulations also suggest that the gap obtained between the two estimators in the context of the new Phillips curve can more readily be accounted for by mis-specification, than by the finite-sample biases.Rational-expectation model ; GMM estimator ; ML estimator ; Inflation ; New Phillips curve

Testing for a Forward-Looking Phillips Curve. Additional Evidence from European and US Data.

The "New Keynesian" Phillips Curve (NKPC) states that inflation has a purely forward-looking dynamics. In this paper, we test whether European and US inflation dynamics can be described by this model. For this purpose, we estimate hybrid Phillips curves, which include both backward and forward-looking components, for major European countries, the euro area, and the US. Estimation is performed using the GMM technique as well as the ML approach. We examine the sensitivity of the results to the choice of output gap or marginal cost as the driving variable, and test the stability of the obtained specifications. Our findings can be summarized as follows. First, in all countries, the NKPC has to be augmented by additional lags and leads of inflation, in contrast to the prediction of the core model. Second, the fraction of backward-looking price setters is large (in most cases, more than 50 percent), suggesting only limited differences between the US and the euro area. Finally, our preferred specification includes marginal cost in the case of the US and the UK, and output gap in the euro area.Forward-looking ; Phillips curve ; euro area ; GMM estimator ; ML estimator.

Assessing GMM Estimates of the Federal Reserve Reaction Function.

Estimating a forward-looking monetary policy rule by the Generalized Method of Moments (GMM) has become a popular approach since the influential paper by Clarida, Gali, and Gertler (1998). However, an abundant econometric literature underlines the unappealing small-samples properties of GMM estimators. Focusing on the Federal Reserve reaction function, we assess GMM estimates in the context of monetary policy rules. First, we show that three usual alternative GMM estimators yield substantially different results. Then, we compare the GMM estimates with two Maximum-Likelihood (ML) estimates, obtained using a small model of the economy. We use Monte-Carlo simulations to investigate the empirical results. We find that the GMM are biased in small sample, inducing an overestimate of the inflation parameter. The two-step GMM estimates are found to be rather close to the ML\ estimates. By contrast, iterative and continuous-updating GMM procedures produce more biased and more dispersed estimators.Forward-looking model ; monetary policy reaction function ; GMM estimator, FIML estimator ; small-sample properties of an estimator.

Modelisation et prevision des indices de prix sectoriels.

Ce papier presente une modelisation de l'indice des prix francais. L'objectif est de permettre une analyse rapide et detaillee des tendances de court terme de l'inflation ainsi que de realiser des previsions a intervalles rapproches. Les caracteristiques de cet outil sont les suivantes: un petit nombre d'equations, une frequence mensuelle, un detail sectoriel assez fin et la publication d'intervalles de confiance relatifs a la prevision.Modèles economiques ; Prevision ; Instrument de mesure ; Prix

Genetic parameters of the twisted legs syndrome in broiler chickens

International audienc

Influence possible des protozoaires sur le taux de mortalité des bactéries autotrophes nitrifiantes

Le modèle de l'IAWQ du processus de boues activées représente les mécanismes endogènes de la biomasse nitrifiante par le décès des micro-organismes (équation d'ordre 1 par rapport à la biomasse). La constante de décès, ou taux de mortalité bA, est aujourd'hui encore mal connue, et en particulier les facteurs influants sur sa valeur. De récentes études ont montré que la prédation par la microfaune pourrait être un facteur déterminant sur la valeur de bA. Cette étude se propose donc de quantifier l'effet de la prédation sur la valeur de bA. Deux réacteurs maintenus sans alimentation en substrat ont été caractérisés en parallèle: l'un a reçu une dose d'antibiotique spécifique aux eucaryotes (cycloheximide) afin de diminuer la quantité d'organismes de la microfaune, alors que l'autre n'a reçu aucun antibiotique (témoin). Les résultats obtenus montrent que le cycloheximide inhibe la plupart des organismes de la microfaune sauf les amibes; celles-ci semblent plutôt stimulées par cet antibiotique. En ce qui concerne la nitrification, un ralentissement de la production de nitrate dans le réacteur traité à l'antibiotique est observé à partir du sixième jour. Cette diminution de production de nitrate est probablement causée par une réduction de l'azote nitrifiable (qui est mobilisé par les amibes) couplée à une prédation des organismes nitrifiants par les amibes. D'ailleurs, l'augmentation de la prédation par les amibes à partir du jour 6 a diminué l'activité nitrifiante également mesurée par respirométrie (rO2 Nmax). Cette diminution du taux de respiration indique une augmentation du taux de mortalité (bA) des organismes nitrifiants. En effet, la valeur du taux de mortalité mesurée dans le réacteur témoin est de 0.08 d-1 alors que selon la microfaune présente dans le réacteur inhibé au cycloheximide, la valeur de ce taux de mortalité a varié entre 0.05 d-1 et 0.15 d-1.Designing biological wastewater treatment plants with the aid of the model developed by the IAWQ requires the knowledge of biological kinetic parameters. For nitrifying activated sludge, these parameters are related to nitrifying bacteria: maximum autotrophic growth rate µAmax, yield coefficient YA and the autotrophic decay rate bA. Although variables influencing µAmax and YA values are well known, this is not the case for bA. MARTINAGE and PAUL (2000) have recently shown that the bA value is strongly influenced by the influent quality, leading to the assumption that influent quality has a strong effect on microfauna composition, and consequently on the grazing rate of microfauna on nitrifying bacteria. In fixed-film processes, protozoan grazing reduces the bacterial population considerably (NATUSCKA and WELANDER, 1994). However, although many data are available concerning the grazing rates of different protozoa, the effect of microfaunal grazing on nitrification is still a matter of debate (RATSAK et al., 1994) and its effect on the bA value is still unknown. These two topics are investigated here.Nitrifying activated sludges were grown in two identical batch reactors, but in one, cycloheximide was added to inhibit eucaryotic growth (MAURINES CARBONEILL et al., 1998). Microfauna organism numbers were quantified in both reactors by microscopic observations of flagellated protozoa (>8 µm), amoebae, ciliates, rotifers and higher invertebrates (Fig. 3). Microbial counts were then correlated with the bA value. The latter was determined using the procedure proposed by SALZER (1992) which consists of characterising the time behaviour of the maximum nitrification rate measured by respirometry of activated sludge under substrate starvation. Under these conditions bacteria die and organic nitrogen is released into the bulk phase. This nitrogen is ammonified, and nitrifying bacteria use this substrate to produce nitrate, and then autotrophic bacterial growth occurs. This method takes this growth into account by characterising nitrate production during the experiment (Fig. 2).The effect of cycloheximide on nitrification was first determined to make sure that this compound is not inhibitory toward nitrifiers. Results obtained (Table 1) show that cycloheximide was not inhibitory toward nitrate production or the maximum nitrification oxygen uptake rate (rO2 N) after 4 hours of contact with nitrifying biomass. Cycloheximide addition in the activated sludge had an important impact on rotifers and flagellates but no effect on ciliates; it also seemed to stimulate amoebae growth. In both reactors, flagellates were mainly Peranama, attached ciliates were mainly Opercularia and Epistylis and a few Vorticella. Free ciliates like Aspidisca and Euplotes were found in both reactors.Variation with time of the abundance of microfauna organisms is shown in Figures 4 and 5 for both reactors. In the reference reactor the number of microfauna organisms decreased with time (Fig. 4) probably due to substrate starvation. Microfauna composition remained however diversified. For the inhibited reactor (Fig. 5), three periods were observed. During period I, the microfauna was mainly composed of ciliates and the number of microfaunal organisms decreased rapidly. During period II, an important growth of amoebae was observed. Cycloheximide was then added during this period to reduce their number. This growth of amoebae seems to be caused by the resistance of these micro-organisms toward inhibiting compounds (SRIKANTH et BERK, 1993). During period III, the number of microfaunal organisms was lower than during period II, and microfauna was mainly composed of ciliates.Nitrate concentration behaviour, necessary for bA calculation, is shown on Figure 6. In the reference reactor, nitrate concentrations varied linearly. For the inhibited reactor, the linear pattern was not observed during period II. This result was probably caused by an important nitrogen assimilation need of amoebae (ELDRIGE and JACKSON, 1993). Because organic nitrogen released by bacterial decay is consumed by amoebae assimilation, less nitrogen is available for the ammonification process and therefore for nitrification. Ammonia concentrations remained below 0.2 mg N·l-1 during all the experiment for both reactors. When amoebae disappeared from the inhibited reactor (period III) nitrate concentration varied linearly again.Variations of the maximum nitrification oxygen uptake rate (rO2 Nmax) with time are presented in Figure 7 (A&B) for both reactors. Two curves are plotted on each figure. Empty squares represent the measured rO2 N and black points represent the maximum nitrification rate that would have been measured if no growth on ammonification products had occurred. For the reference reactor (Fig. 7A), a value for bA of 0.08 d-1 can be calculated and can be considered constant for a constant microfauna composition.Three bA values can be estimated for the reactor inhibited with cycloheximide (Fig. 7B), corresponding to the three periods observed for microfauna composition. During period I, the bA value is 0.05 d-1 : a decrease in the microfaunal organism numbers implies a decrease of the bA value. During period II, when a development of amoebae is observed, the bA value increases and reaches 0.15 d-1. During period III with reduced grazing, the bA value is 0.13 d-1. Since during periods I and III the microfauna is mainly composed of ciliates, this difference between bA values is likely due to the observed difference in floc size between periods I and III.The results obtained during this study tend to prove (1) that the use of cycloheximide reduces microfaunal populations but can lead to a development of amoebae, and (2) that microfauna grazing seems to have an influence on the bA value, which can vary from 0.05 to 0.15 d-1 depending on microfaunal composition and abundance

Rational invariants of even ternary forms under the orthogonal group

In this article we determine a generating set of rational invariants of minimal cardinality for the action of the orthogonal group $\mathrm{O}_3$ on the space $\mathbb{R}[x,y,z]_{2d}$ of ternary forms of even degree $2d$. The construction relies on two key ingredients: On one hand, the Slice Lemma allows us to reduce the problem to dermining the invariants for the action on a subspace of the finite subgroup $\mathrm{B}_3$ of signed permutations. On the other hand, our construction relies in a fundamental way on specific bases of harmonic polynomials. These bases provide maps with prescribed $\mathrm{B}_3$-equivariance properties. Our explicit construction of these bases should be relevant well beyond the scope of this paper. The expression of the $\mathrm{B}_3$-invariants can then be given in a compact form as the composition of two equivariant maps. Instead of providing (cumbersome) explicit expressions for the $\mathrm{O}_3$-invariants, we provide efficient algorithms for their evaluation and rewriting. We also use the constructed $\mathrm{B}_3$-invariants to determine the $\mathrm{O}_3$-orbit locus and provide an algorithm for the inverse problem of finding an element in $\mathbb{R}[x,y,z]_{2d}$ with prescribed values for its invariants. These are the computational issues relevant in brain imaging.Comment: v3 Changes: Reworked presentation of Neuroimaging application, refinement of Definition 3.1. To appear in "Foundations of Computational Mathematics

Analytic Metaphysics versus Naturalized Metaphysics: The Relevance of Applied Ontology

The relevance of analytic metaphysics has come under criticism: Ladyman & Ross, for instance, have suggested do discontinue the field. French & McKenzie have argued in defense of analytic metaphysics that it develops tools that could turn out to be useful for philosophy of physics. In this article, we show first that this heuristic defense of metaphysics can be extended to the scientific field of applied ontology, which uses constructs from analytic metaphysics. Second, we elaborate on a parallel by French & McKenzie between mathematics and metaphysics to show that the whole field of analytic metaphysics, being useful not only for philosophy but also for science, should continue to exist as a largely autonomous field