Empirical likelihood confidence regions for comparison distributions and roc curves

Abstract: The authors derive empirical likelihood confidence regions for the comparison distribution of two populations whose distributions are to be tested for equality using random samples. Another application they consider is to ROC curves, which are used to compare measurements of a diagnostic test from two populations. The authors investigate the smoothed empirical likelihood method for estimation in this context, and empirical likelihood based confidence intervals are obtained by means of the Wilks theorem. A bootstrap approach allows for the construction of confidence bands. The method is illustrated with data analysis and a simulation study.     

On Broadening Failure Rate Distributions in PRA Uncertainty Analyses

Several recent nuclear power plant probabilistic risk assessments (PRAs) have utilized broadened Reactor Safety Study (RSS) component failure rate population variability curves to compensate for such things as expert "overvaluation bias" in the estimates upon which the curves are based.
A simple two-components of variation empirical Bayes model is proposed for use in estimating the between-expert variability curve in the presence of such biases. Under certain conditions this curve is a population variability curve. Comparisons are made with the existing method.
The popular procedure appears to be generally much more conservative than the empirical Bayes method in removing such biases. In one case the broadened curve based on the popular method is more than two orders of magnitude broader than the empirical Bayes curve. In another case it is found that the maximum justifiable degree of broadening of the RSS curve is to increase α from 5% to 12%, which is significantly less than the 20% value recommended in the popular approach.     

The South Oaks Gambling Screen-revised Adolescent (SOGS-RA) Revisited: A Cut-point Analysis

The lack of a criterion validity gold standard defining adolescent pathological gambling represents a major limitation of the adolescent gambling literature. The present study employed Receiver Operating Characteristic curve analysis (ROC) to examine the performance of the South Oaks Gambling Screen-Revised Adolescent (SOGS-RA) recommended cut-point of 4 against two-proxy gold standards: self-identified need for, or receipt of, help for gambling. Logistic regression analysis examined the correlates of self-identified need for help with gambling. The sample was comprised of 12990 adolescents from Atlantic Canada whose average age was 15 years and 50% of whom were male. The SOGS-RA performed as well or better with these proxy gold standards than with proxies used in previous studies. We concluded that the proxy gold standards based on self-identified need for or receipt of help represent a pragmatic solution to the lack of an adolescent-specific definition of problem or pathological gambling. Students in grade seven and SOGS-RA scores of 4 or greater were independent predictors of self-identifying a need for help.     

Optimal cutoffs for continuous biomarkers for survival data under competing risks

Identifying an optimal cutoff value for a continuous biomarker is often useful for medical applications. For binary outcome, commonly used cutoff finding criteria include Youden's index, classification accuracy, and the Euclidean distance to the upper left corner on the ROC curve. We extend these three criteria to accommodate censored survival time that subjected to competing risks. We provide various definitions of time-dependent true positive rate and false positive rate and estimate those quantities using nonparametric methods. In simulation studies, the Euclidean distance to the upper left corner on the ROC curve shows the best overall performance.     

Local principal differential analysis: Graphical methods for functional data with covariates

We focus on principal differential analysis (PDA) of functional data for obtaining a low-dimensional representation of a collection of curves. PDA assumes there exists a linear differential operator that results in the zero-function when it is applied to each of the data curves, or equivalently, that the curves belong to a low-dimensional subspace of a normed linear space. PDA sets out to estimate this linear differential operator from the data and proceeds from there. Our contribution is to explain how subject covariates can be incorporated into a PDA analysis for graphical exploration of patterns in the data.     

Improving the biomarker diagnostic capacity via functional transformations

The use of the area under the receiver-operating characteristic, ROC, curve (AUC) as an index of diagnostic accuracy is overwhelming in fields such as biomedical science and machine learning. It seems that a larger AUC value has become synonymous with a better performance. The functional transformation of the marker values has been proposed in the specialized literature as a procedure for increasing the AUC and therefore the diagnostic accuracy. However, the classification process is based on some regions (classification subsets) which support the decision made; one subject is classified as positive if its marker is within this region and classified as negative otherwise. In this paper we study the capacity of improving the classification performance of univariate biomarkers via functional transformations and the impact of this transformation on the final classification regions based on a real-world dataset. Particularly, we consider the problem of determining the gender of a subject based on the Mode frequency of his/her voice. The shape of the cumulative distribution function of this characteristic in both the male and the female groups makes the resulting classification problem useful for illustrating the differences between having useful diagnostic rules and obtaining an optimal AUC value. Our point is that improving the AUC by means of a functional transformation can produce classification regions with no practical interpretability. We propose to improve the classification accuracy by making the selection of the classification subsets more flexible while preserving their interpretability. Besides, we provide different graphical approximations which allow us a better understanding of the classification problem.     

我国财政挤出效应的定量研究

扩张性财政政策的可持续性与挤出效应的强弱密切相关 ,我国实施扩张性的积极财政政策 ,是否对私人投资产生挤出效应引起国内外研究者高度关注 ,理论界对此观点不一 ,尚缺乏定量研究。依据我国经济实际运行的规律和数据 ,运用经济计量学的方法 ,我们可以具体测算出中国的IS—LM曲线以及财政政策的挤出效应和挤入效应的大小。     

Selection and combination of biomarkers using ROC method for disease classification and prediction

Based on the SCAD penalty and the area under the ROC curve (AUC), we propose a new method for selecting and combining biomarkers for disease classification and prediction. The proposed estimator for the combination of the biomarkers has an oracle property; that is, the estimated combination of the biomarkers performs as well as it would have been if the biomarkers significantly associated with the outcome had been known in advance, in terms of discriminative power. The proposed estimator is computationally feasible, n^1/2‐consistent and asymptotically normal. Simulation studies show that the proposed method performs better than existing methods. We illustrate the proposed methodology in the acoustic startle response study. The Canadian Journal of Statistics 39: 324–343; 2011 © 2011 Statistical Society of Canada     

Nonparametric maximum likelihood estimation for shifted curves

The analysis of a sample of curves can be done by self-modelling regression methods. Within this framework we follow the ideas of nonparametric maximum likelihood estimation known from event history analysis and the counting process set-up. We derive an infinite dimensional score equation and from there we suggest an algorithm to estimate the shape function for a simple shape invariant model. The nonparametric maximum likelihood estimator that we find turns out to be a Nadaraya–Watson-like estimator, but unlike in the usual kernel smoothing situation we do not need to select a bandwidth or even a kernel function, since the score equation automatically selects the shape and the smoothing parameter for the estimation. We apply the method to a sample of electrophoretic spectra to illustrate how it works.