A Structured Expert Judgment Study for a Model of Campylobacter Transmission During Broiler-Chicken Processing

A structured expert judgment study was organized to obtain input data for a microbial risk-assessment model describing the transmission of campylobacter during broiler-chicken processing in the Netherlands. More specially, the expert study was aimed at quantifying the uncertainty on input parameters of this model and focused on the contamination of broiler-chicken carcasses with campylobacter during processing. Following the protocol for structured expert judgment studies, expert assessments were elicited individually through subjective probability distribution functions. The classical model was used to aggregate the individual experts' distributions in order to obtain a single combined distribution per variable. Three different weighting schemes were applied, including equal weighting and performance-based weighting with and without optimalization of the combined distributions. The individual experts' weights were based on their performance on the seed variables. Results of the various weighting schemes are presented in terms of performance, robustness, and combined distributions of the seed variables and some of the query variables. All three weighting schemes had adequate performance, with the optimized combined distributions significantly outperforming both the equal weight and the nonoptimized combined distributions. Hence, this weighting scheme, having adequate robustness, was chosen for further processing of the results.     

Estimation with Interval Censored Data and Covariates

In biostatistical applications interest often focuses on the estimation of the distribution of time T between two consecutive events. If the initial event time is observed and the subsequent event time is only known to be larger or smaller than an observed monitoring time C, then the data conforms to the well understood singly-censored current status model, also known as interval censored data, case I. Additional covariates can be used to allow for dependent censoring and to improve estimation of the marginal distribution of T. Assuming a wrong model for the conditional distribution of T, given the covariates, will lead to an inconsistent estimator of the marginal distribution. On the other hand, the nonparametric maximum likelihood estimator of FT requires splitting up the sample in several subsamples corresponding with a particular value of the covariates, computing the NPMLE for every subsample and then taking an average. With a few continuous covariates the performance of the resulting estimator is typically miserable. In van der Laan, Robins (1996) a locally efficient one-step estimator is proposed for smooth functionals of the distribution of T, assuming nothing about the conditional distribution of T, given the covariates, but assuming a model for censoring, given the covariates. The estimators are asymptotically linear if the censoring mechanism is estimated correctly. The estimator also uses an estimator of the conditional distribution of T, given the covariates. If this estimate is consistent, then the estimator is efficient and if it is inconsistent, then the estimator is still consistent and asymptotically normal. In this paper we show that the estimators can also be used to estimate the distribution function in a locally optimal way. Moreover, we show that the proposed estimator can be used to estimate the distribution based on interval censored data (T is now known to lie between two observed points) in the presence of covariates. The resulting estimator also has a known influence curve so that asymptotic confidence intervals are directly available. In particular, one can apply our proposal to the interval censored data without covariates. In Geskus (1992) the information bound for interval censored data with two uniformly distributed monitoring times at the uniform distribution (for T has been computed. We show that the relative efficiency of our proposal w.r.t. this optimal bound equals 0.994, which is also reflected in finite sample simulations. Finally, the good practical performance of the estimator is shown in a simulation study. This revised version was published online in July 2006 with corrections to the Cover Date.     

The EM Algorithm—an Old Folk-song Sung to a Fast New Tune

Celebrating the 20th anniversary of the presentation of the paper by Dempster, Laird and Rubin which popularized the EM algorithm, we investigate, after a brief historical account, strategies that aim to make the EM algorithm converge faster while maintaining its simplicity and stability (e.g. automatic monotone convergence in likelihood). First we introduce the idea of a 'working parameter' to facilitate the search for efficient data augmentation schemes and thus fast EM implementations. Second, summarizing various recent extensions of the EM algorithm, we formulate a general alternating expectation–conditional maximization algorithm AECM that couples flexible data augmentation schemes with model reduction schemes to achieve efficient computations. We illustrate these methods using multivariate t -models with known or unknown degrees of freedom and Poisson models for image reconstruction. We show, through both empirical and theoretical evidence, the potential for a dramatic reduction in computational time with little increase in human effort. We also discuss the intrinsic connection between EM-type algorithms and the Gibbs sampler, and the possibility of using the techniques presented here to speed up the latter. The main conclusion of the paper is that, with the help of statistical considerations, it is possible to construct algorithms that are simple, stable and fast.     

Recurrent events analysis in the presence of time-dependent covariates and dependent censoring

Summary.  Recurrent events models have had considerable attention recently. The majority of approaches show the consistency of parameter estimates under the assumption that censoring is independent of the recurrent events process of interest conditional on the covariates that are included in the model. We provide an overview of available recurrent events analysis methods and present an inverse probability of censoring weighted estimator for the regression parameters in the Andersen–Gill model that is commonly used for recurrent event analysis. This estimator remains consistent under informative censoring if the censoring mechanism is estimated consistently, and it generally improves on the naïve estimator for the Andersen–Gill model in the case of independent censoring. We illustrate the bias of ad hoc estimators in the presence of informative censoring with a simulation study and provide a data analysis of recurrent lung exacerbations in cystic fibrosis patients when some patients are lost to follow-up.     

Is Fertility Behavior in Our Genes? Findings from a Danish Twin Study

This article investigates the fertility of Danish twins born during the periods 1870–1910 and 1953–64 in order to pursue two central questions for understanding human reproduction: Do genetic dispositions influence fertility and fertility-related behavior? Does the relevance of the “nature versus nurture” debate shift over time or with demographic regimes? The authors find that genetic influences on fertility exist, but that their relative magnitude and pattern are contingent on gender and on the socioeconomic environment experienced by cohorts. Among females born in 1880–90 and after 1955, about 30–50 percent of the variance in fertility is due to genetic influences; these influences are substantially smaller for earlier and for interim birth cohorts. Male fertility is generally subject to smaller genetic and larger shared-environment effects than female fertility. Because genetic effects are most prevalent in situations with deliberately controlled fertility and relatively egalitarian socioeconomic opportunities, the authors propose that the genetic dispositions affect primarily fertility behavior and motivations for having children. Analyses of fertility motivations, measured by age of first attempt to have a child, support this interpretation.     

争取食品权的国际人权

在人权中具体讨论人类有关食品的权利有利于促进了人权理论在学术界的发展(Craven,1995年,第110-114页)。对此,本篇论文首先介绍了有关人权法学理论的一般发展状况,并在此基础上重点强调了食品权利的发展以及两者之间的相互作用。此外,人权发展不仅体现出国际特色、国家特色,也因为欧盟这些区域组织的作用而颇具区域特色,为此本文也论述了欧盟对于人权和食品权的落实和保障情况。     

A versatile bivariate distribution on a bounded domain: another look at the product moment correlation

The Farlie-Gumbel-Morgenstern (FGM) family has been investigated in detail for various continuous marginals such as Cauchy, normal, exponential, gamma, Weibull, lognormal and others. It has been a popular model for the bivariate distribution with mild dependence. However, bivariate FGMs with continuous marginals on a bounded support discussed in the literature are only those with uniform or power marginals. In this paper we study the bivariate FGM family with marginals given by the recently proposed two-sided power (TSP) distribution. Since this family of bounded continuous distributions is very flexible, the properties of the FGM family with TSP marginals could serve as an indication of the structure of the FGM distribution with arbitrary marginals defined on a compact set. A remarkable stability of the correlation between the marginals has been observed.     

Sexual inactivity among men who have sex with men living with hiv in europe

Objectives: Most people living with HIV stay sexually active, but some remain inactive. This study investigated prevalence and correlates of sexual inactivity among European HIV-positive men who have sex with men (MSM). Methods: An anonymous sexual health questionnaire was distributed in 17 HIV outpatient clinics throughout Europe. Ninety-seven (11.6%) of 838 respondents reported absence of sexual activity. Results: Multivariable regression analysis identified older age, relationship status, and less satisfaction with general health and sexual desire as being associated with sexual inactivity. Conclusions: Prevalence of sexual inactivity has declined since the introduction of antiretroviral therapy to levels similar to those of HIV-negative MSM, suggesting a tendency toward normalization of HIV-positive MSM's sex lives.     

Economic evaluation of brief sex counseling for sexually dysfunctional adolescents

Objectives: In a randomized controlled trial brief sex counselling (BSC), intensive sexual healthcare (ISH) and no treatment (NT) for adolescents with a sexual dysfunction were compared. The aim of this study was to assess the cost-effectiveness and cost-utility of BSC versus ISH and NT from a societal perspective. Methods: Costs, sexual functioning and quality of life were measured during 6 months. Primary outcome measures were measured with the Female Sexual Functional Index, the International Index of Erectile Function and the utilities reflecting Quality of Life based on the SF-36. Uncertainty was dealt with by using bootstrap replications and sensitivity analyses. Results: Results show that the societal costs were the highest for ISH followed by NT and BSC. The difference in costs between ISH compared to NT and BSC was significant. Furthermore, there were no significant group differences in sexual functioning or quality of life. With respect to the cost-effectiveness and cost-utility, BSC can be considered to be a suitable treatment for adolescents with a sexual dysfunction. Conclusions: Due to the lack of a significant difference in clinical effect, it can be concluded that BSC is the cheapest treatment option when implementing the intention-to-treat, besides a no treatment option, for adolescents with a sexual dysfunction.     

Practising Gender When Networking: The Case of University–Industry Innovation Projects

This paper gains insight into the role of gender in interpersonal networks, which is largely neglected in research on networking. We do so by exploring the concept of ‘practising gender’, the spatial‐temporal accomplishment of gender practices, when people build, maintain and exit social networks. The paper is based on a study of male‐dominated technological collaboration projects between universities and industry. Our analysis of observations of project meetings and interviews with project participants demonstrates how people in real time and space draw from culturally available gender practices in their networking with each other. This practising of gender was found to be done largely unreflexively, sometimes through humour, within allegedly trivial activities such as pouring coffee and socializing as well as in critical activities such as composing the network. The exploration of the practising of gender in relation to culturally available gender practices enabled us to examine how those gender practices are reproduced, stretched or challenged when people network. We show how focussing on the dynamic side of gender allows us to get better insight into how gender inequalities in networks are reproduced or countered on the micro‐interactional level.