Knowledge that Transforms

Pseudo maximum likelihood techniques are applied to basic Poisson models and to Poisson models with specification errors. In the latter case it is shown that consistent and asymptotically normal estimators can be obtained without specifying the p.d.f. of the disturbances. These estimators are compared both from the finite sample and the asymptotic point of view. Quasi generalized PML estimators, which asymptotically dominate all PML estimators, are also proposed. Finally, bivariate and panel data Poisson models are discussed. THE ANALYSIS OF ECONOMIC BEHAVIOR often leads to the study of characteristics taking a small number of positive values. The classical linear model is not adapted to explain how such discrete variables depend on other quantitative or qualitative variables. The reasons are similar to those usually given in the case of an endogenous qualitative variable: the shape of the observation set does not correspond to a linear model, the assumption of normality of the disturbances cannot be made, since the endogenous variables take a small number of values with strictly positive probabilities, and the prediction formulae which are deduced from a linear model give impossible values. In the models considered in the literature to describe discrete variables (Cox and Lewis [2], El. Sayyad [3], Frome, Kutner, and Beauchamp [4], Gilbert [5], Hausman, Hall, and Griliches [8]; see also Lancaster [12]) the endogenous variable is assumed to have a Poisson distribution conditional upon the exogenous variables. The parameter of this distribution is a function of the values of the exogenous variables. The choice of such a model is justified if the dependent variable counts the occurrence of a given event during a fixed period and if the usual assumptions of the Poisson process are satisfied. For instance, the model is adapted to describe daily numbers of oil tankers' arrivals in a port, the number of accidents at work by factory, or the number of patents applied for and received by firms (Hausman, Hall, and Griliches [8]).

Agricultural and Food Policy, Research Methods/Statistical Methods

[We consider the nature of the inferences that can be made when all variables in a linear regression are measured with error. Assuming that the measurement errors are orthogonal to each other and the unobserved correctly measured regressors, we demonstrate that the true regression coefficient vector can be restricted to the convex hull of all possible regressions iff all these regressions yield coefficient vectors lying in the same orthant. Otherwise, the set of feasible coefficient vectors is unbounded. For the unbounded case, we demonstrate that prior information concerning the "seriousness" of the measurement errors in the variables can bound the feasible region. Two diagnostics are proposed to indicate the sensitivity of conventional inferences to measurement error in the regressors, and an illustrative example is presented.]

We specify and estimate a small fix-price model with quantity rationing on both the goods and labor markets. The side of the market which is rationed is random. The model is able to generate a productivity cycle and the degree of capacity utilization is endogenous. The rationing scheme, allocating supply between the various components of demand is estimated. The probabilities of being in the various regimes, the intensity of the disequilibrium on the markets, and the results of policy exercises are discussed.

"This paper discusses two approaches that economists have taken in analyzing the timing of births. It formulates an empirical model appropriate for one of these approaches and demonstrates its usefulness using household survey data from Costa Rica. The hazard rate technique employed in this paper is a natural way of modeling a broad class of problems where the occurrence of an event is uncertain." The study also indicates that "historical data can be used to determine whether the strong trend in the relationship between regional mortality levels and the age at first birth is real or the result of inappropriate data. Additionally, data from other countries might be employed to determine whether the significant effect of male education levels on the risk of subsequent births is a general result. Finally..., the predictions of theoretical models dealing with the number and pace of births can be tested using data from younger women."