A note on the estimation of linear regression models with Heteroskedastic measurement errors

I consider the estimation of linear regression models when the independent variables are measured with errors whose variances differ across observations, a situation that arises, for example, when the explanatory variables in a regression model are estimates of population parameters based on samples of varying sizes. Replacing the error variance that is assumed common to all observations in the standard errors-in-variables estimator by the mean measurement error variance yields a consistent estimator in the case of measurement error heteroskedasticity. However, another estimator, which I call the Heteroskedastic Errors in Variables Estimator (HEIV), is, under standard assumptions, asymptotically more efficient. Simulations show that the efficiency gains are likely to appreciable in practice. In addition, the HEIV estimator, which is equal to the ordinary least squares regression of the dependent variable on the best linear predictor of the true independent variables, is simple to compute with standard regression software.Regression analysis

The persistence of the Chekanov-Eliashberg algebra

We apply the barcodes of persistent homology theory to the Chekanov-Eliashberg algebra of a Legendrian submanifold to deduce displacement energy bounds for arbitrary Legendrians. We do not require the full Chekanov-Eliashberg algebra to admit an augmentation as we linearize the algebra only below a certain action level. As an application we show that it is not possible to $C^0$-approximate a stabilized Legendrian by a Legendrian that admits an augmentation.Comment: 29 pages, 4 figures; version accepted for publication in Selecta Mathematica. This is a major revision with many fixes and improvements. The constant in Theorem 1.1 has been improved. The theory of barcodes have been properly introduced in the new Section 2 together with new related terminology. The proof of Theorem 1.1 was rewritten in the new language and given a greater level of detail

Recent trends in job displacement

Displaced workers ; Job security ; Unemployment

EBIC investigation of hydrogenation of crystal defects in EFG solar silicon ribbons

Changes in the contrast and resolution of defect structures in 205 Ohm-cm EFG polysilicon ribbon subjected to annealing and hydrogenation treatments were observed in a JEOL 733 Superprobe scanning electron microscope, using electron beam induced current (EBIC) collected at an A1 Schottky barrier. The Schottky barrier was formed by evaporation of A1 onto the cleaned and polished surface of the ribbon material. Measurement of beam energy, beam current, and the current induced in the Schottky diode enabled observations to be quantified. Exposure to hydrogen plasma increased charge collection efficiency. However, no simple causal relationship between the hydrogenation and charge collection efficiency could be inferred, because the collection efficiency also displayed an unexpected thermal dependence. Good quality intermediate-magnification (1000X-5400X) EBIC micrographs of several specific defect structures were obtained. Comparison of grown-in and stress-induced dislocations after annealing in vacuum at 500 C revealed that stress-induced dislocations are hydrogenated to a much greater degree than grown-in dislocations. The theoretical approximations used to predict EBIC contrast and resolution may not be entirely adequate to describe them under high beam energy and low beam current conditions

Manufacturing plants’ use of temporary workers: an analysis using census micro data

Using plant-level data from the Plant Capacity Utilization (PCU) Survey, we examine how a manufacturing plant’s use of temporary workers is associated with the nature of its output fluctuations. Our empirical evidence suggests that plants choose temps over perms when they expect output to fall, which allows them to avoid costs associated with laying off permanent employees. We also found that plants whose output levels are associated with greater levels of uncertainty use more temps. The effects of other variables are also tested in order to examine the validity of various views about why firms use temporary workers. The variables we look at include wage and benefit levels for permanent workers, unionization rates, turnover rates, seasonal factors, and plant size and age.Temporary employees