Assessing accuracy of a continuous screening test in the presence of verification bias

Summary.  In studies to assess the accuracy of a screening test, often definitive disease assessment is too invasive or expensive to be ascertained on all the study subjects. Although it may be more ethical or cost effective to ascertain the true disease status with a higher rate in study subjects where the screening test or additional information is suggestive of disease, estimates of accuracy can be biased in a study with such a design. This bias is known as verification bias. Verification bias correction methods that accommodate screening tests with binary or ordinal responses have been developed; however, no verification bias correction methods exist for tests with continuous results. We propose and compare imputation and reweighting bias-corrected estimators of true and false positive rates, receiver operating characteristic curves and area under the receiver operating characteristic curve for continuous tests. Distribution theory and simulation studies are used to compare the proposed estimators with respect to bias, relative efficiency and robustness to model misspecification. The bias correction estimators proposed are applied to data from a study of screening tests for neonatal hearing loss.     

中国近30 年来的农村改革发展历程回顾与展望

文章重点从农村改革的整体性、综合性、协调性和党在农村政策的稳定性、连续性、实效性等方面入手,把我国近30年来的农村改革发展历程划分为三个不同的时期:即从1978年到1988年,是农村改革的起步阶段,出现了第一个“黄金发展期”;从1988年到1998年,是农村改革的停滞阶段,出现了“三农综合症”;从1998年10月至今,是农村改革的快速推进阶段,出现了第二个“黄金发展期”。全面准确地认识和把握我国农村改革的历史进程,对于科学制定农村综合改革的整体方案及相关配套政策措施至关重要。     

《金锁记》改写的背后

《金锁记》是张爱玲作品中唯一一篇充满斗争激越、呼应“五四”主题的文章。改写后的《怨女》则成为超越时代局限 ,走向人性深处 ,带有普泛性和恒定性主题的文章。在张爱玲的文学趣味向传统复归的背后 ,是作者对“五四”文学的反思 ,以及对中国文艺的表现方式、表现题材的寻求。     

论人与自然的本原性和谐--自然之所以美的一个重要原因

以往的种种自然美理论 ,特别是“自然人化”说都程度不同地忽略了自然之所以美的一个重要原因 :人与自然的本原性和谐。它是人与自然的一种主要由血缘决定的自然而然、发自内心、不言自明、近似本能性的特殊的情感关系。“黄金时代”史前研究为其奠定了史前史的发生学基础 ,“归依体验”理论为其提供了审美心理学的印证 ,“回归自然”的主张和实际行动为其出具了历史实践证明 ,著名思想家的代表性论述为其积累了极富启迪的思想资料。     

亚里士多德的"德性就是中道"思想解读--读《尼各马科伦理学》有感

亚里士多德的《尼各马科伦理学》是其伦理学思想的代表作,书中阐述的重要内容之一:“德性就是中道”,具有丰富的内涵,体现了与德性相关的选择性、实践理性以及与社会性生活密切相关等特点。这些对当代道德教育仍有一定的启迪意义。     

Record-breaking data: a parametric comparison of the inverse-sampling and the random-sampling schemes

In many industrial quality control experiments and destructive stress testing, the only available data are successive minima (or maxima)i.e., record-breaking data. There are two sampling schemes used to collect record-breaking data: random sampling and inverse sampling. For random sampling, the total sample size is predetermined and the number of records is a random variable while in inverse-sampling the number of records to be observed is predetermined; thus the sample size is a random variable. The purpose of this papper is to determinevia simulations, which of the two schemes, if any, is more efficient. Since the two schemes are equivalent asymptotically, the simulations were carried out for small to moderate sized record-breaking samples. Simulated biases and mean square errors of the maximum likelihood estimators of the parameters using the two sampling schemes were compared. In general, it was found that if the estimators were well behaved, then there was no significant difference between the mean square errors of the estimates for the two schemes. However, for certain distributions described by both a shape and a scale parameter, random sampling led to estimators that were inconsistent. On the other hand, the estimated obtained from inverse sampling were always consistent. Moreover, for moderated sized record-breaking samples, the total sample size that needs to be observed is smaller for inverse sampling than for random sampling.     

A new estimator of proportion with a linear function using data from two-decks randomized response model

A new estimator for estimating the proportion of a potentially sensitive attribute in survey sampling has been introduced by solving a linear equation. The proposed estimator has been compared with the estimator proposed by Odumade and Singh (2009) with equal protection to all of the respondents. The asymptotic properties of the proposed estimator are investigated through exact numerical illustrations for different choices of parameters. A non randomized response approach has been suggested. A scope for further research has also been pointed out.     

Estimation of Mode Using Two-phase Sampling

In this article, we consider the problem of estimation of mode using two-phase sampling. Ratio- and difference-type estimators in two-phase sampling are proposed. The asymptotic properties of the proposed estimators are studied analytically as well as empirically for different situations for the given cost of surveys. The use of two-phase sampling has been found to be cost saving design while estimating mode by making a proper use of auxiliary information.     

Quasi-minimax estimation in the partial linear model

This article discusses the minimax estimator in partial linear model y = Zβ + f + ε under ellipsoidal restrictions on the parameter space and quadratic loss function. The superiority of the minimax estimator over the two-step estimator is studied in the mean squared error matrix criterion.     

Classical estimation of hazard rate and mean residual life functions of Pareto distribution

Abstract

In this paper we find the maximum likelihood estimates (MLEs) of hazard rate and mean residual life functions (MRLF) of Pareto distribution, their asymptotic non degenerate distribution, exact distribution and moments. We also discuss the uniformly minimum variance unbiased estimate (UMVUE) of hazard rate function and MRLF. Finally, two numerical examples with simulated data and real data set, are presented to illustrate the proposed estimates.