Finite-Sample Inference Methods for Simultaneous Equations and Models with Unobserved and Generated Regressors

We propose finite sample tests and confidence sets for models with unobserved and generated regressors as well as various models estimated by instrumental variables methods. The validity of the procedures is unaffected by the presence of identification problems or \"weak instruments\", so no detection of such problems is required. We study two distinct approaches for various models considered by Pagan (1984). The first one is an instrument substitution method which generalizes an approach proposed by Anderson and Rubin (1949) and Fuller (1987) for different (although related) problems, while the second one is based on splitting the sample. The instrument substitution method uses the instruments directly, instead of generated regressors, in order to test hypotheses about the \"structural parameters\" of interest and build confidence sets. The second approach relies on \"generated regressors\", which allows a gain in degrees of freedom, and a sample split technique. For inference about general possibly nonlinear transformations of model parameters, projection techniques are proposed. A distributional theory is obtained under the assumptions of Gaussian errors and strictly exogenous regressors. We show that the various tests and confidence sets proposed are (locally) \"asymptotically valid\" under much weaker assumptions. The properties of the tests proposed are examined in simulation experiments. In general, they outperform the usual asymptotic inference methods in terms of both reliability and power. Finally, the techniques suggested are applied to a model of Tobin’s q and to a model of academic performance.

Identification, Weak Instruments and Statistical Inference in Econometrics

We discuss statistical inference problems associated with identification and testability in econometrics, and we emphasize the common nature of the two issues. After reviewing the relevant statistical notions, we consider in turn inference in nonparametric models and recent developments on weakly identified models (or weak instruments). We point out that many hypotheses, for which test procedures are commonly proposed, are not testable at all, while some frequently used econometric methods are fundamentally inappropriate for the models considered. Such situations lead to ill-defined statistical problems and are often associated with a misguided use of asymptotic distributional results. Concerning nonparametric hypotheses, we discuss three basic problems for which such difficulties occur: (1) testing a mean (or a moment) under (too) weak distributional assumptions; (2) inference under heteroskedasticity of unknown form; (3) inference in dynamic models with an unlimited number of parameters. Concerning weakly identified models, we stress that valid inference should be based on proper pivotal functions —a condition not satisfied by standard Wald-type methods based on standard errors — and we discuss recent developments in this field, mainly from the viewpoint of building valid tests and confidence sets. The techniques discussed include alternative proposed statistics, bounds, projection, split-sampling, conditioning, Monte Carlo tests. The possibility of deriving a finite-sample distributional theory, robustness to the presence of weak instruments, and robustness to the specification of a model for endogenous explanatory variables are stressed as important criteria assessing alternative procedures.

Prédication vs détermination: l'exemple de la fonction adverbiale

info:eu-repo/semantics/published

Les techniques du dinandier: formes et fonction des outils lithiques spécifiques à la déformation plastique des métaux

In recent years, the proliferation of discoveries has enabled studies of stone tools used in metal working to develop. The increasing number of tools, made mostly from Neolithic polished axes, reveals a typological and functional diversity that remained largely unsuspected. This diversity is an opportunity to understand the tools and address the technical issues relating to the plastic deformation of metals. The operations that are represented here demonstrate the techniques used by coppersmiths with specialised tools.

Prothèses totales d'épaules inversées : récupérer la fonction en cas d'incompétence de la coiffe des rotateurs

Les principales caractéristiques biomécaniques de la prothèse inversée (cupule sur le versant huméral et sphère sur le versant scapulaire), cet implant semi-contraint, consistent en une médialisation ainsi qu'un abaissement du centre de rotation. Par ce biais, le bras de levier du deltoïde est augmenté. Les fibres musculaires du deltoïde antérieur et postérieur sont ainsi également recrutées pour devenir principalement abducteur. La congruence relative des composants (semi-contrainte) confère également à la prothèse inversée une certaine stabilité primaire, importante pour pallier la déficience de la coiffe des rotateurs (sus-épineux).

Estimation non paramétrique d'une fonction d'évaluation d'options avec contraintes de monotonie et de convexité.

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Influence de l'emploi relatif dans la fonction publique sur le taux d'emploi : le cas des provinces canadiennes.

Rapport de recherche

Test de l'hypothèse de revenu permanent et anticipations rationnelles avec présence d'une rupture dans la fonction de tendance.

Rapport de recherche