Estimation Under the Lehmann Regression Model with Interval-Censored Data

We consider the estimation problem under the Lehmann model with interval-censored data, but focus on the computational issues. There are two methods for computing the semi-parametric maximum likelihood estimator (SMLE) under the Lehmann model (or called Cox model): the Newton-Raphson (NR) method and the profile likelihood (PL) method. We show that they often do not get close to the SMLE. We propose several approach to overcome the computational difficulty and apply our method to a breast cancer research data set.     

A generalized model of logistic regression for clustered data

This paper proposes a generalized logistic regression model that can account for the correlation among responses on subunits. The subunits may arise as data on multiple observations within an individual. This method generalizes earlier work by Rosner (1984 a,b) and others. Methodological generalizations include: (1) the use of the more general Polya-Eggenberger distribution instead of the beta-binomial distribution to model the correlation structure, so that cases with negative, positive, or zero intraclass correlation can be handled; (2) a stepwise approach; (3) linear and non-linear regression; and, (4) the inclusion of the case of a truncated distribution. The model can accommodate missing data and covariates on the unit and subunit level. The derivative-free simplex algorithm is used to estimate the parameters.

The model is applied to data describing the progression of obstruction in coronary disease where multiple arterial segments are studied for each patient. The correlation in response that may exist for these multiple segments is accounted for in the analyses while attempting to examine associations with individual-specific (e.g., history of diabetes) and segment-specific (e.g., initial percent stenosis) covariates. Analyses were performed on a data set describing 382 patients with unoperated coronary artery disease and two coronary angiograms separated by at least one month and on a data set describing 284 patients undergoing percutaneous transluminal coronary angioplasty and studied by coronary angiograms.     

Estimators for a simultaneous equation model with lagged endogenous variables and autocorrelated errors

Two full information estimators and a limited information estimator for the simultaneous equation model with autocorrelated errors are studies by the Monte Carlo method.The estimators share features of the two-step Gauss-Newton procedure and of Aitken generalized least squares.One full information method generates the estimated endogenous variables used in the later stages of computation from the unrestricted reduced form while the other uses a restricted reduced form.The observed small sample behavior was close to that suggested by asymptotic theory.     

别让高薪CEO带来低绩效

薪酬一旦与绩效考核脱节，就会导致董事会成员的不负责任。这样的董事会可能会将企业和员工置于一个危险的境地。近日来，公众对企业CEO过高薪酬的反对与愤怒可谓愈演愈烈。这并不是没有原因的。有太多的CEO即使在绩效低下的情况下，仍然可以按时拿到数目不菲的高额薪水。     

Regression models for analyzing clustered binary and continuous outcomes under an assumption of exchangeability

Scientific experiments commonly result in clustered discrete and continuous data. Existing methods for analyzing such data include the use of quasi-likelihood procedures and generalized estimating equations to estimate marginal mean response parameters. In applications to areas such as developmental toxicity studies, where discrete and continuous measurements are recorded on each fetus, or clinical ophthalmologic trials, where different types of observations are made on each eye, the assumption that data within cluster are exchangeable is often very reasonable. We use this assumption to formulate fully parametric regression models for clusters of bivariate data with binary and continuous components. The regression models proposed have marginal interpretations and reproducible model structures. Tractable expressions for likelihood equations are derived and iterative schemes are given for computing efficient estimates (MLEs) of the marginal mean, correlations, variances and higher moments. We demonstrate the use the ‘exchangeable’ procedure with an application to a developmental toxicity study involving fetal weight and malformation data.     

Southern two-lined salamanders in urbanizing watersheds

Forested riparian buffers are an increasingly common method of mitigating the negative effects of impervious surface cover on water quality and wildlife habitat. We sampled larval southern two-lined salamanders (Eurycea cirrigera) in 43 streams, representing the range of impervious surface cover and forested riparian buffer width across Wake County, NC, USA. Larval abundance decreased with increasing impervious surface cover in the upstream catchment, but was not affected by buffer width. This is likely a result of an incomplete buffer system and culverts or other breaches along streams. Larval abundance increased with detritus cover in the stream to a threshold and then decreased as detritus continued to increase. As percent pebble substrate in the stream increased, especially in perennial streams, larval salamander abundance also increased. We suspect salamanders were unable to migrate with the water column during dry periods in intermittent streams with sedimented interstices below the surface, resulting in low abundances. A combination of increased peak flows and sedimentation, reduced base flow, and chemical changes likely reduces the abundance of salamanders in urban and suburban streams. We suggest creation of catchment-wide, unbreached buffers to maintain the integrity of stream habitats in urbanizing watersheds.     

Fund-raising models at public historically Black colleges and universities

This empirical study examined whether public historically Black colleges and universities (HBCUs) predominantly practiced the press agentry, public information, two-way asymmetrical, two-way symmetrical or mixed motive models of fund raising. The findings reported the heavy usage of press agentry model of fund raising by advancement officers. The most interesting concept emerging from the research was the emergence of a mixed motive model of fund raising. The model describes the practice of fund raising in an adaptable and changing environment and incorporates asymmetrical and symmetrical tactics that describes the actual practice of fund raising.     

"BY PUBLIC OPINION I MEAN"--

"Where all people talk on the same subject, they should be agreedabout the vocabulary with which they discuss it: or, at anyrate, they should be aware that they are not agreed."     

A machine learning analysis of drought and rural population change on the North American Great Plains since the 1970s

Population and Environment - Machine learning techniques have to date not been widely used in population-environment research, but represent a promising tool for identifying relationships between...