434 resultados para Validité prédictive
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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.
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Conditional heteroskedasticity is an important feature of many macroeconomic and financial time series. Standard residual-based bootstrap procedures for dynamic regression models treat the regression error as i.i.d. These procedures are invalid in the presence of conditional heteroskedasticity. We establish the asymptotic validity of three easy-to-implement alternative bootstrap proposals for stationary autoregressive processes with m.d.s. errors subject to possible conditional heteroskedasticity of unknown form. These proposals are the fixed-design wild bootstrap, the recursive-design wild bootstrap and the pairwise bootstrap. In a simulation study all three procedures tend to be more accurate in small samples than the conventional large-sample approximation based on robust standard errors. In contrast, standard residual-based bootstrap methods for models with i.i.d. errors may be very inaccurate if the i.i.d. assumption is violated. We conclude that in many empirical applications the proposed robust bootstrap procedures should routinely replace conventional bootstrap procedures for autoregressions based on the i.i.d. error assumption.
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It is well known that standard asymptotic theory is not valid or is extremely unreliable in models with identification problems or weak instruments [Dufour (1997, Econometrica), Staiger and Stock (1997, Econometrica), Wang and Zivot (1998, Econometrica), Stock and Wright (2000, Econometrica), Dufour and Jasiak (2001, International Economic Review)]. One possible way out consists here in using a variant of the Anderson-Rubin (1949, Ann. Math. Stat.) procedure. The latter, however, allows one to build exact tests and confidence sets only for the full vector of the coefficients of the endogenous explanatory variables in a structural equation, which in general does not allow for individual coefficients. This problem may in principle be overcome by using projection techniques [Dufour (1997, Econometrica), Dufour and Jasiak (2001, International Economic Review)]. AR-types are emphasized because they are robust to both weak instruments and instrument exclusion. However, these techniques can be implemented only by using costly numerical techniques. In this paper, we provide a complete analytic solution to the problem of building projection-based confidence sets from Anderson-Rubin-type confidence sets. The latter involves the geometric properties of “quadrics” and can be viewed as an extension of usual confidence intervals and ellipsoids. Only least squares techniques are required for building the confidence intervals. We also study by simulation how “conservative” projection-based confidence sets are. Finally, we illustrate the methods proposed by applying them to three different examples: the relationship between trade and growth in a cross-section of countries, returns to education, and a study of production functions in the U.S. economy.
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This paper employs the one-sector Real Business Cycle model as a testing ground for four different procedures to estimate Dynamic Stochastic General Equilibrium (DSGE) models. The procedures are: 1 ) Maximum Likelihood, with and without measurement errors and incorporating Bayesian priors, 2) Generalized Method of Moments, 3) Simulated Method of Moments, and 4) Indirect Inference. Monte Carlo analysis indicates that all procedures deliver reasonably good estimates under the null hypothesis. However, there are substantial differences in statistical and computational efficiency in the small samples currently available to estimate DSGE models. GMM and SMM appear to be more robust to misspecification than the alternative procedures. The implications of the stochastic singularity of DSGE models for each estimation method are fully discussed.
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"Mémoire présenté à la Faculté des études supérieures en vue de l'obtention du grade de maîtrise en droit (LL.M.) (Option: droit des affaires )"
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"Mémoire présenté à la Faculté des études supérieures en vue de l'obtention du grade de maîtrise en droit (LL.M.)"
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"Mémoire présenté à la Faculté des études supérieures en vue de l'obtention du grade de maître en droit LL.M."
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Le principal reproche qui est adressé au droit international est la faiblesse de ses mécanismes de sanctions. Pour cette raison, plusieurs penseurs juridiques ont conclu que le droit international n'existait pas. Le présent mémoire vise donc à étudier la rhétorique derrière cette affirmation et à examiner sa validité. Pour ce faire, nous analysons dans un premier temps la relation entre la sanction et le droit à travers le cadre positiviste du XIXe siècle. Nous étudions tour à tour les soi-disant critères constitutifs de la sanction. Nous les comparons avec d'autres ordres non juridiques pour ensuite rejeter le postulat positiviste qui fait de la contrainte et de la centralisation des pouvoirs les éléments essentiels de la sanction. Nous étudions ensuite le cadre d'adoption des sanctions économiques du Conseil de sécurité des Nations Unies. Cette étape nous permet d'expliquer les principales faiblesses et limitations du droit international. Parmi celles-ci, le manque de coopération internationale, le droit de veto et le principe de la souveraineté nationale sont les éléments qui freinent l'adoption des sanctions coopération internationale. Nous examinons ensuite les objectifs derrière l'imposition des sanctions ainsi que leur efficacité. Finalement, nous étudions les embargos en général et les embargos sur les armes. Cette étude nous permet d'une part de démontrer les effets des sanctions économiques sur la population civile et sur les États tiers. D'autre part, elle nous permet de mieux comprendre les problèmes relatifs à l'administration d'une sanction, ainsi qu'aux mesures de contournement des interdictions.
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"Mémoire présenté à la Faculté des études supérieures en vue de l'obtention du grade de LL.M. en droit option droit des affaires"
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"Mémoire présenté à la faculté des études supérieures en vue de l'obtention du grade de maîtrise en droit (LL.M.)"