A class of partially linear single‐index survival models

The authors define a class of “partially linear single‐index” survival models that are more flexible than the classical proportional hazards regression models in their treatment of covariates. The latter enter the proposed model either via a parametric linear form or a nonparametric single‐index form. It is then possible to model both linear and functional effects of covariates on the logarithm of the hazard function and if necessary, to reduce the dimensionality of multiple covariates via the single‐index component. The partially linear hazards model and the single‐index hazards model are special cases of the proposed model. The authors develop a likelihood‐based inference to estimate the model components via an iterative algorithm. They establish an asymptotic distribution theory for the proposed estimators, examine their finite‐sample behaviour through simulation, and use a set of real data to illustrate their approach.     

Non-parametric recursive estimates of a probability density function and its derivatives

Recursive estimates of a probability density function (pdf) are known. This paper presents recursive estimates of a derivative of any desired order of a pdf. Let f be a pdf on the real line and p?0 be any desired integer. Based on a random sample of size n from f, estimators f^(p)_n of f^(p), the pth order derivatives of f, are exhibited. These estimators are of the form $\text{n}{}^{\mathrm{?1}}\text{∑n}\text{j=1}\text{δ}{}_{\mathrm{jp}}$, where δ_jp depends only on p and the jth observation in the sample, and hence can be computed recursively as the sample size increases. These estimators are shown to be asymptotically unbiased, mean square consistent and strongly consistent, both at a point and uniformly on the real line. For pointwise properties, the conditions on f^(p) have been weakened with a little stronger assumption on the kernel function.     

IMPACT OF SEAT BELT USE ON DRIVING BEHAVIOR

Previous research has indicated that individual compensating behavior, specifically, more risky driving may reduce the effectiveness of seat belt laws. We test the compensating-behavior hypothesis using individual-specific survey data. The analysis also incorporates individual risk tastes. Our results indicate that the compensating-behavior hypothesis applies only to those that are not strongly risk averse. Other risk-differentiated groups do not exhibit compensating behavior. Finally, it seems that individuals learn to reduce compensating behavior over time.     

Successful strategies—The story of Singapore Airlines (SIA)

This case study describes the growth and development of Singapore Airlines from a small national carrier serving the Malayan States to an international airline with a network extending to 27 countries. Its strategy is simple: quality service at a competitive price, made possible by high investment in equipment and in staff training.     

A NOTE ON OPTIMUM STRATIFICATION FOR EQUAL ALLOCATION WITH RATIO AND REGRESSION METHODS OF ESTIMATION

When the information on a highly positively correlated auxiliary variable x is used to construct stratified regression (or ratio) estimates of the population mean of the study variable y, the paper considers the problem of determining approximately optimum strata boundaries (AOSB) on x when the sample size in each stratum is equal. The form of the conditional variance function V(y/x) is assumed to be known. A numerical investigation into the relative efficiency of equal allocation with respect to the Neyman and proportional allocations has also been made. The relative efficiency of equal allocation with respect to Neyman allocation is found to be nearly equal to one.     

Pension reform, the stock market, capital formation and economic growth: A critical commentary on the World Bank's proposals

Proposing far-reaching reforms to pension systems, the World Bank has recently suggested that the existing pay-as-you-go systems in many rich as well as poor countries should be replaced by fully funded, mandatory, preferably private pensions, as the main pillars of the new system. It argues that these reforms will not only benefit pensioners but also enhance savings, and promote capital formation and economic development. This paper provides a critical examination of the Bank's theses and concludes that it has adopted a one-sided view of the relationships between the key critical variables. The proposed reform may therefore neither protect the old nor achieve faster economic growth.     

A note on the asymptotic optimality of a two population sequential probability ratio test

It is shown that a two population sequential probability ratio test studied by a number of recent authors in the context of sequential medical trials is asymptotically optimal.     

Contextual and ideological dimensions of attitudes toward discretionary abortion

This study examines the contextual and ideological dimensions of attitudes toward discretionary abortion using two national surveys. The abortion attitudes are dichotomized in terms of consistent opposition versus consistent support. Discriminant analysis, partial correlations, and stepwise regression procedures are used in the analysis. Findings indicate that education and attendance at religious services are the two most significant contextual dimensions and sexual permissiveness and fertility ideology are the two most significant ideological dimensions for explaining attitudes toward discretionary abortion. Implications of these findings are discussed.     

Efficient Algorithms for Determining 3-D Bi-Plane Imaging Geometry

Biplane projection imaging is one of the primary methods for imaging and visualizing the cardiovascular system in medicine. A key problem in such a technique is to determine the imaging geometry (i.e., the relative rotation and translation) of two projections so that the 3-D structure can be accurately reconstructed. Based on interesting observations and efficient geometric techniques, we present in this paper new algorithmic solutions for this problem. Comparing with existing optimization-based approaches, our techniques yield better accuracy and have bounded execution time, thus is more suitable for on-line applications. Our techniques can easily detect outliers to further improve the accuracy.This research was supported in part by NIH under USPHS grant numbers HL52567.     

A NOTE ON SAMPLE QUANTILE PROCESSES OF FINITE POPULATIONS

A representation is established for sample quantile processes of simple random samples drawn without replacement from finite populations. The result is then used to obtain weak limits of properly normalized quantile processes and their linear functions.