Efficient rank tests for semiparametric competing risk models

We consider a semiparametric competing risk model given by k independent survival times. The paper offers an asymptotic treatment of tests for the semiparametric null hypothesis of equality of the underlying risks. It turns out that modified rank tests are asymptotically efficient for certain semiparametric submodels, where the baseline hazard is a nuisance parameter. In addition, the asymptotic relative efficiency of the present tests is derived. A comparison of asymptotic power functions can then be used to classify various tests proposed earlier in the literature. For instance a chi-square type test is efficient for proportional hazards. Data driven tests of likelihood ratio type are proposed for cones of alternatives. We will consider certain stochastically increasing alternatives as a special example. The paper shows how the concept of local asymptotic normality of Le Cam works for hazard oriented models.     

Block recursion and structural vector autoregressions

In applications of structural VAR modeling, finite-sample properties may be difficult to obtain when certain identifying restrictions are imposed on lagged relationships. As a result, even though imposing some lagged restrictions makes economic sense, lagged relationships are often left unrestricted to make statistical inference more convenient. This paper develops block Monte Carlo methods to obtain both maximum likelihood estimates and exact Bayesian inference when certain types of restrictions are imposed on the lag structure. These methods are applied to two examples to illustrate the importance of imposing restrictions on lagged relationships.     

基于Gibbs采样的MIMO信号检测改进算法

针对传统Gibbs采样算法的“失控问题”,提出了一种改进算法,在Gibbs迭代采样过程中加入对噪声方差的估计,消除了失控问题。设计了信号检测流程,将最大似然（ML）检测的搜索过程嵌入Gibbs迭代采样过程,减少了最大似然检测的计算步骤。仿真结果表明,所提算法能估计噪声方差,具有接近最大似然检测的性能。     

Pareto Index Estimation Under Moderate Right Censoring

Real claim data sometimes are censored from above at a high value induced by the sum insured. In this note we examine the behaviour of extreme-value methods in such settings and propose an adaptation of the popular Hill (1975) estimator. It is argued that the censoring typically cannot exceed 5% for an effective use of the methods suggested.     

Trust Promoting Seals in Electronic Markets

Abstract

In order to promote web sales, companies conducting electronic commerce are constantly seeking viable and efficient ways to increase web traffic. One approach is to build consumers' trust, and ultimately to increase web sales. Many business-to-consumer online merchants follow this approach and display trust-promoting seals on their websites. However, whether these seals really fulfill the tasks they have promised has remained unexplored. This study empirically examines the influence of trust-promoting seals on consumers' online purchasing decisions. The results show that the trust-promoting seals are generally effective in promoting web sales, and some seals enhance promotion better than others.     

GMM estimation of a maximum entropy distribution with interval data

We develop a generalized method of moments (GMM) estimator for the distribution of a variable where summary statistics are available only for intervals of the random variable. Without individual data, one cannot calculate the weighting matrix for the GMM estimator. Instead, we propose a simulated weighting matrix based on a first-step consistent estimate. When the functional form of the underlying distribution is unknown, we estimate it using a simple yet flexible maximum entropy density. Our Monte Carlo simulations show that the proposed maximum entropy density is able to approximate various distributions extremely well. The two-step GMM estimator with a simulated weighting matrix improves the efficiency of the one-step GMM considerably. We use this method to estimate the U.S. income distribution and compare these results with those based on the underlying raw income data.     

The impact of MAS on perceived auditor independence-some evidence from Denmark

The Enron case has highlighted that the provision of management advisory services (MAS) can endanger auditor independence. Recently, a number of changes have not only been made to the relevant international and US regulations, but also to the Danish regulations in this area. Theoretical research explains the emergence of non-independence and demonstrates that the provision of MAS can decrease independence. According to the economic model of DeAngelo, the existence of client-specific quasi-rents impairs auditor independence. The provision of MAS increases quasi-rents and thus, is a threat to independence. Antle used an agency theoretical approach. Information asymmetries between auditor and client could lead to a moral hazard risk, i.e. the auditor could give up independence from client's management and accept payments for withholding detected errors and irregularities. The client's management could also use MAS to legally compensate the auditor for giving away independence.A large number of empirical studies have investigated the influence of MAS on the perceived independence of the auditor. Most of these studies were performed in English speaking countries and the majority found a negative impact. Sociological research reveals cultural differences between English speaking and Nordic countries, e.g. concerning the dimension ‘masculinity’. Thus, an empirical investigation of the impact of MAS on perceived auditor independence in Denmark is promising. It was found that shareholders, bank loan officers and journalists perceive a negative effect on auditor independence if MAS are provided. The recent liberalization in Denmark is inconsistent with this finding. Furthermore, it was shown that the type of MAS influences the degree to which auditor independence is perceived to be impaired. Thus, independence rules related to MAS should be differentiated. Additionally, the study ascertained that perceived auditor independence does not increase if MAS are provided by a separate department of the audit firm. An internal separation of the auditing and the consulting function within the same audit firm is not viewed as being beneficial in Denmark.     

Two state capital accumulation with heterogenous products: Disruptive vs. non-disruptive goods

The paper considers the problem of a firm that, while producing a standard product, has the option to introduce an innovative product. The innovative product competes with the standard product and will therefore reduce revenues of the standard product. A distinction is made between innovative products that do or do not become even more relatively appealing as their market share grows (e.g., because of network externalities). It is shown that in the former case, which we call a “disruptive” good, history dependent long run equilibria can occur, which are in line with recent real life economic examples.     

A new proof of the maximum principle

Summary. We offer a new proof of the maximum principle, by using the envelope theorem that is frequently used in the standard microeconomic theory. Received: April 11, 2002; revised version: June 26, 2002 Correspondence to: K. Shimomura     

Parametric Robust Test for Several Variances with Unknown Underlying Distributions

Tsou (in comm Stat-Theor Math 32: 2013–2019, 2003) proposed a parametric robust procedure for testing the equality of two population variances. With large samples the proposed test remains valid under model misspecification. In this article the robust technique is further extended to the comparison of several population variances. More specifically the score test derived on the basis of normal models is adjusted to become robust. The adjusted robust test provides asymptotically valid inference so long as the true underlying distributions have finite fourth moments. Unlike most robust nonparametric approaches, this novel robust technique too provides legitimate variance estimates for estimators of the interested parameters.