Penalized and Shrinkage Estimation in the Cox Proportional Hazards Model

This article considers the shrinkage estimation procedure in the Cox's proportional hazards regression model when it is suspected that some of the parameters may be restricted to a subspace. We have developed the statistical properties of the shrinkage estimators including asymptotic distributional biases and risks. The shrinkage estimators have much higher relative efficiency than the classical estimator, furthermore, we consider two penalty estimators—the LASSO and adaptive LASSO—and compare their relative performance with that of the shrinkage estimators numerically. A Monte Carlo simulation experiment is conducted for different combinations of irrelevant predictors and the performance of each estimator is evaluated in terms of simulated mean squared error. Simulation study shows that the shrinkage estimators are comparable to the penalty estimators when the number of irrelevant predictors in the model is relatively large. The shrinkage and penalty methods are applied to two real data sets to illustrate the usefulness of the procedures in practice.     

Inference under Heteroscedasticity of Unknown Form Using an Adaptive Estimator

The heteroscedasticity consistent covariance matrix estimators are commonly used for the testing of regression coefficients when error terms of regression model are heteroscedastic. These estimators are based on the residuals obtained from the method of ordinary least squares and this method yields inefficient estimators in the presence of heteroscedasticity. It is usual practice to use estimated weighted least squares method or some adaptive methods to find efficient estimates of the regression parameters when the form of heteroscedasticity is unknown. But HCCM estimators are seldom derived from such efficient estimators for testing purposes in the available literature. The current article addresses the same concern and presents the weighted versions of HCCM estimators. Our numerical work uncovers the performance of these estimators and their finite sample properties in terms of interval estimation and null rejection rate.     

Probabilistic Properties of Parametric Dual and Inverse Time Series Models Generated by ARMA Models

For the class of autoregressive-moving average (ARMA) processes, we examine the relationship between the dual and the inverse processes. It is demonstrated that the inverse process generated by a causal and invertible ARMA (p, q) process is a causal and invertible ARMA (q, p) model. Moreover, it is established that this representation is strong if and only if the generating process is Gaussian. More precisely, it is derived that the linear innovation process of the inverse process is an all-pass model. Some examples and applications to time reversibility are given to illustrate the obtained results.     

Stabilizing the Performance of Kurtosis Estimator of Multivariate Data

The estimation of the kurtosis parameter of the underlying distribution plays a central role in many statistical applications. The central theme of the article is to improve the estimation of the kurtosis parameter using a priori information. More specifically, we consider the problem of estimating kurtosis parameter of a multivariate population when some prior information regarding the the parameter is available. The rationale is that the sample estimator of the kurtosis parameter has a large estimation error. In this situation we consider shrinkage and pretest estimation methodologies and reappraise their statistical properties. The estimation based on these strategies yield relatively smaller estimation error in comparison with the sample estimator in the candidate subspace. A large sample theory of the suggested estimators are developed and compared. The results demonstrate that suggested estimators outperform the estimator based on the sample data only in the candidate subspace. In an effort to appreciate the relative behavior of the estimators in a finite sample scenario, a Monte-carlo simulation study is planned and performed. The result of simulation study strongly corroborates the asymptotic result. To illustrate the application of the estimators, some example are showcased based on recently published data.     

纪念苏丹商人穆罕默德·哈吉在华首设商务处

中国与阿拉伯非洲的历史交往源远流长,特别是与苏丹的联系,可以追溯到西汉时期,而且从那时起双方之间的往来一直延续不断.本文在历史回顾的基础上,通过实地调查和口传资料,着重考察了19世纪末苏丹商人穆罕默德·哈吉在广州首设商务办事处并开展苏(丹)中(国)贸易、加强双方社会联系的历史活动,揭示了苏中悠久关系史上鲜为人知的一页.     

Reflections on conducting research on the ‘war on terror’: religious identity,subjectivity and emotions

In recent years there has been an increase in literature which has explored the insider/outsider position through ethnic identities. However, there remains a neglect of religious identities, even though it could be argued that religious identities have become increasingly important through being prominent in international issues such as the ‘war on terror’ and the Middle East conflict. Through drawing on the concept of subjectivity, I reflect on research I conducted on the impact of the ‘war on terror’ on British Muslims. I explore the space between the insider/outsider position demonstrating how my various subjectivities – the ‘non-Islamic appearance I’, the ‘Muslim I’, the ‘personal I’, the ‘exploring I’, the ‘Kashmiri I’ or the ‘Pakistani I’, the ‘status I’ and the ‘outsider I’ – assisted in establishing trust, openness and commonality. I conclude by demonstrating how the ‘emotional I’ allowed me to manage my own emotions and participants emotions.     

Evaluating the Cost,Safety, and Proliferation Risks of Small Floating Nuclear Reactors

It is hard to see how our energy system can be decarbonized if the world abandons nuclear power, but equally hard to introduce the technology in nonnuclear energy states. This is especially true in countries with limited technical, institutional, and regulatory capabilities, where safety and proliferation concerns are acute. Given the need to achieve serious emissions mitigation by mid‐century, and the multidecadal effort required to develop robust nuclear governance institutions, we must look to other models that might facilitate nuclear plant deployment while mitigating the technology's risks. One such deployment paradigm is the build‐own‐operate‐return model. Because returning small land‐based reactors containing spent fuel is infeasible, we evaluate the cost, safety, and proliferation risks of a system in which small modular reactors are manufactured in a factory, and then deployed to a customer nation on a floating platform. This floating small modular reactor would be owned and operated by a single entity and returned unopened to the developed state for refueling. We developed a decision model that allows for a comparison of floating and land‐based alternatives considering key International Atomic Energy Agency plant‐siting criteria. Abandoning onsite refueling is beneficial, and floating reactors built in a central facility can potentially reduce the risk of cost overruns and the consequences of accidents. However, if the floating platform must be built to military‐grade specifications, then the cost would be much higher than a land‐based system. The analysis tool presented is flexible, and can assist planners in determining the scope of risks and uncertainty associated with different deployment options.     

Preservation properties for the mean residual life ordering

Sereral preservation results for the mean residual life (mr) ordering are given. In particular, we show that the mr-ordering is preserved under convolutions, mixtures and weak convergence.     

Financial Contracting,Governance Structures and the Accounting Regulation of Islamic Banks: An Analysis in Terms of Agency Theory and Transaction Cost Economics

Because Islamic banks are prohibited from entering into transactions based on riba (interest), they mobilise funds mainly on the basis of the mudaraba (profit-sharing) form of contract. Thus, in the place of interest-bearing customer deposits, Islamic banks offer investment accounts the return on which depends on the return on the pool of assets in which the customers' funds are invested by the bank. In contrast to conventional deposits, such investment accounts therefore yield a variable periodic return which may be negative (a loss). Islamic investment accounts are thus a form of limited-duration equity investment.This type of investment account raises a set of issues concerning the contractual relations between the bank and the holders of such investment accounts. These issues may be addressed from the perspectives of both Agency Theory (principal-agent and principal-principal relations) and Transaction Cost Economics (contractual forms and governance structures), and it is the purpose of this paper to do so. In particular, we focus on governance issues such as the monitoring possibilities which may or may not be contractually available to investment account holders. We conclude that, under present contractual arrangements, investment account holders depend unduly upon 'vicarious' monitoring by or on behalf of shareholders, a situation aggravated by current shortcomings in financial reporting and limitations of the scope of external auditing. The latter have implications for accounting regulation as applied to Islamic banks. The paper concludes with some suggestions as to how this situation could be ameliorated.