Endogenous Sampling in Duration Models

This paper considers the problem of endogenous sampling in the duration model. This is an important problem in the duration analysis of bank failures and loan defaults because it is common for the researchers in these areas to use only the default sample or non-default sample or both at a certain ratio, rather than using a random sample. The properties of endogenous sampling have been considered in various models, notably in qualitative response models, but not in duration models as far as I am aware. In this paper, I obtain the asymptotic distribution of the endogenous sampling maximum likelihood estimator and compare it with that of the random sampling maximum likelihood estimator and indicate when efficiency gain may result. I also show that the random sampling maximum likelihood estimator is inconsistent if the data are collected by endogenous sampling.

Quark Confinement Physics in Quantum Chromodynamics

We study abelian dominance and monopole condensation for the quark confinement physics using the lattice QCD simulations in the MA gauge. These phenomena are closely related to the dual superconductor picture of the QCD vacuum, and enable us to construct the dual Ginzburg-Landau (DGL) theory as an useful effective theory of nonperturbative QCD. We then apply the DGL theory to the studies of the low-lying hadron structure and the scalar glueball properties.Comment: Talk given at 15th International Conference on Particle and Nuclei (PANIC 99), Uppsala, Sweden, 10-16 Jun 1999, 4 page

Endogenous Sampling and Matching Method in Duration Models

Endogenous sampling with matching (also called gmixed samplingh) occurs when the statistician samples from the non-right- censored subset at a predetermined proportion and matches on one or more exogenous variables when sampling from the right-censored subset. This is widely applied in the duration analysis of firm failures, loan defaults, insurer insolvencies, and so on, due to the low frequency of observing non-right-censored samples (bankrupt, default, and insolvent observations in respective examples). However, the common practice of using estimation procedures intended for random sampling or for the qualitative response model will yield either an inconsistent or inefficient estimator. This paper proposes a consistent and efficient estimator and investigates its asymptotic properties. In addition, this paper evaluates the magnitude of asymptotic bias when the model is estimated as if it were a random sample or an endogenous sample without matching. This paper also compares the relative efficiency of other commonly used estimators and provides a general guideline for optimally choosing sample designs. The Monte Carlo study with a simple example shows that random sampling yields an estimator of poor finite sample properties when the population is extremely unbalanced in terms of default and non-default cases while endogenous sampling and mixed sampling are robust in this situation.Duration models; Endogenous sampling with matching; Maximum likelihood estimator; Manski-Lerman estimator; Asymptotic distribution

Instantons and Monopoles in the Nonperturbative QCD

We study the confinement physics in QCD in the maximally abelian (MA) gauge using the SU(2) lattice QCD. To clarify the origin of abelian dominance for the long-range physics, we study the charged-gluon propagator in the lattice QCD, and find that the effective mass $m_{ch} \simeq 0.9 {\rm GeV}$ of the charged gluon is induced by the MA gauge fixing. In the MA gauge, there appears the global network of the monopole world-line covering the whole system, which would be identified as monopole condensation at a large scale. To prove monopole condensation, we apply the dual gauge formalism to the monopole part, and derive the inter-monopole potential from the dual Wilson loop in the MA gauge. In the monopole part, which carries the nonperturbative aspects of QCD, the dual gluon mass is evaluated as $m_B \simeq$0.5GeV, which is the evidence of the dual Higgs mechanism by monopole condensation. As for the monopole structure, the large fluctuation of off-diagonal gluons remains around the monopole in the MA gauge, and large cancellation occurs between the diagonal and off-diagonal action densities to keep the total QCD action finite. The charged-gluon rich region around the QCD-monopole would provide the effective monopole size as the critical scale of the abelian projected QCD. Instantons are expected to appear in the charged-gluon rich region around the monopole world-line in the MA gauge, which leads to the local correlation between monopoles and instantons.Comment: Invited Lecture presented by H. Suganuma at 1997 Yukawa International Seminar (YKIS'97) on `` Non-Perturbative QCD -Structure of the QCD Vacuum-'', 2-12 December 1997, in Kyoto, Japan, 12 pages, Plain Late

Les circuits courts : Un « monde de commercialisation » interpersonnel ?

Les circuits courts sont souvent analysés en terme de réseaux locaux d'échange servant d'alternative à l'échange marchand standard, en étant caractérisés par l'importance des interactions entre producteurs et consommateurs. Nous allons donc voir dans quelle mesure ces circuits courts peuvent être analysés avec l'outil proposé par Salais et Storper (1993) de "mondes de production". Nous montrerons en particulier qu'ils correspondent au monde interpersonnel. Nous préciserons par la suite les caractéristiques de ce monde, en terme de relations sociales d'échange et en illustrant avec le système japonais du TEIKEI.Vente directe, "Mondes de production", TEIKEI, incertitude, confiance