A simple approach to analyzing clustered longitudinal data

When modeling correlated binary data in the presence of informative cluster sizes, generalized estimating equations with either resampling or inverse-weighting, are often used to correct for estimation bias. However, existing methods for the clustered longitudinal setting assume constant cluster sizes over time. We present a subject-weighted generalized estimating equations scheme that provides valid parameter estimation for the clustered longitudinal setting while allowing cluster sizes to change over time. We compare, via simulation, the performance of existing methods to our subject-weighted approach. The subject-weighted approach was the only method that showed negligible bias, with excellent coverage, for all model parameters.     

Karhunen–Loeve expansion for the additive detrended Brownian motion

In this article, we obtain the Karhunen–Loeve expansion and Pythagorean type distribution identities for the additive detrended Brownian motion. As applications, the corresponding Laplace transform and small-deviation asymptotic behavior for the L₂ norm are given.     

Efficacy of screening and treatment of latent tuberculosis infection

ABSTRACT

Sixty-three percent of the total active tuberculosis cases in Canada were diagnosed among foreign-born individuals, representing 20% of the total population. The majority of these cases occur from the reactivation of tuberculosis infections acquired prior to immigration. A preventive policy consisting of screening and treating new immigrants for latent tuberculosis infection is evaluated on its efficacy for reducing the total number of tuberculosis cases, using tuberculosis incidence data between 1986 and 1995 from the Canadian tuberculosis reporting system. The most effective intervention is to screen for and treat latent tuberculosis infection among arriving immigrants from countries of birth with a tuberculosis incidence rate greater than 15 cases per 100,000.     

线性脉冲微分方程组的渐近性态

研究线性脉冲微分方程组解的渐近性态,揭示脉冲效应对系统解的性态影响,并推广非线性脉冲微分方程组.     

Self-Consistency Estimation of Distributions Based on Truncated and Doubly Censored Survival Data with Applications to AIDS Cohort Studies

Gomez and Lagakos (1994) propose a nonparametric method for estimating the distribution of a survival time when the origin and end points defining the survival time suffer interval-censoring and right-censoring, respectively. In some situations, the end point also suffers interval-censoring as well as truncation. In this paper, we consider this general situation and propose a two-step estimation procedure for the estimation of the distribution of a survival time based on doubly interval-censored and truncated data. The proposed method generalizes the methods proposed by DeGruttola and Lagakos (1989) and Sun (1995) and is more efficient than that given in Gomez and Lagakos (1994). The approach is based on self-consistency equations. The method is illustrated by an analysis of an AIDS cohort study.     

Ownership Structure,Corporate Value and Firm Investment: A Simultaneous Equations Analysis of Spanish Companies

This paper is concerned with the set of mutualrelationships between firm valuation andinvestment, and with the possible endogeneityof ownership structure. In order to deal withthem properly, we aim to test the mutual impactof investment, corporate value and ownership bybroadening the usual framework with asimultaneous equations approach. Using a sampleof 140 Spanish listed companies for the1991–1997 period, we have found that,consistent with previous research, thealignment and entrenchment hypotheses seem tobe confirmed by the estimation of aone-equation model. However, when analyzed bymeans of a system of simultaneous equations inwhich a set of mutual relationships isintroduced, quite different results wereobtained. Although valuation and investment offirms are determined by managerial ownership,we have found that ownership structure may alsobe influenced both by investment and value.Consequently, it is not completely right toinfer that ownership structure determines firmvalue unidirectionally; however the benchmarkshould be broadened so as to take an explicitaccount of the mutual links between firm value,investment and ownership.     

抛物型方程的自适应正交配置算法

本文针对抛物型方程数值解不稳定的问题,利用牛顿迭代法来求解隐式Euler方法所给出的离散格式,获得了数值解较为稳定的抛物型方程自适应正交配置算法.     

Characterizations of generalized mixtures of geometric and exponential distributions based on upper record values

Let X _{U (1)} < X _{U (2)} < … < X _{U ( n )} < … be the sequence of the upper record values from a population with common distribution function F. In this paper, we first give a theorem to characterize the generalized mixtures of geometric distribution by the relation between E[(X _{U ( n +1)}–X _{U ( n )})²|X _{U ( n )} = x] and the function of the failure rate of the distribution, for any positive integer n. Secondly, we also use the same relation to characterize the generalized mixtures of exponential distribution. The characterizing relations were motivated by the work of Balakrishnan and Balasubramanian (1995). Received: March 31, 1999; revised version: November 22, 1999     

A simple method for estimating a regression model for κ between a pair of raters

Agreement studies commonly occur in medical research, for example, in the review of X-rays by radiologists, blood tests by a panel of pathologists and the evaluation of psychopathology by a panel of raters. In these studies, often two observers rate the same subject for some characteristic with a discrete number of levels. The κ-coefficient is a popular measure of agreement between the two raters. The κ-coefficient may depend on covariates, i.e. characteristics of the raters and/or the subjects being rated. Our research was motivated by two agreement problems. The first is a study of agreement between a pastor and a co-ordinator of Christian education on whether they feel that the congregation puts enough emphasis on encouraging members to work for social justice (yes versus no). We wish to model the κ-coefficient as a function of covariates such as political orientation (liberal versus conservative) of the pastor and co-ordinator. The second example is a spousal education study, in which we wish to model the κ-coefficient as a function of covariates such as the highest degree of the father of the wife and the father of the husband. We propose a simple method to estimate the regression model for the κ-coefficient, which consists of two logistic (or multinomial logistic) regressions and one linear regression for binary data. The estimates can be easily obtained in any generalized linear model software program.