Random regression models for human immunodeficiency virus ribonucleic acid data subject to left censoring and informative drop-outs

Objectives in many longitudinal studies of individuals infected with the human immunodeficiency virus (HIV) include the estimation of population average trajectories of HIV ribonucleic acid (RNA) over time and tests for differences in trajectory across subgroups. Special features that are often inherent in the underlying data include a tendency for some HIV RNA levels to be below an assay detection limit, and for individuals with high initial levels or high ranges of change to drop out of the study early because of illness or death. We develop a likelihood for the observed data that incorporates both of these features. Informative drop-outs are handled by means of an approach previously published by Schluchter. Using data from the HIV Epidemiology Research Study, we implement a maximum likelihood procedure to estimate initial HIV RNA levels and slopes within a population, compare these parameters across subgroups of HIV-infected women and illustrate the importance of appropriate treatment of left censoring and informative drop-outs. We also assess model assumptions and consider the prediction of random intercepts and slopes in this setting. The results suggest that marked bias in estimates of fixed effects, variance components and standard errors in the analysis of HIV RNA data might be avoided by the use of methods like those illustrated.     

The value of information in anticipated utility theory

A well-known property of expected utility theory is that the value of information is nonnegative. Given the widespread dissatisfaction with the expected utility hypothesis, a natural question to ask is whether competing theories of choice preserve this property. This article considers one widely discussed alternative to expected utility, anticipated utility theory. We show that, like expected utility, the anticipated value of perfect information is always nonnegative. The value of imperfect information, however, may be negative, though the precise valuation of information depends upon whether the reduction of compound lotteries axiom is used to derive the anticipated utility functional.I am indebted to Edi Karni, Peter Wakker, and an anonymous referee for helpful comments on earlier versions of this article. They are of course in no way responsible for errors or obscurities in the present version.     

Quality Provision with Heterogeneous Consumer Reservation Utilities

This study examines a firm's quality and price decisions when consumers differ not only in their willingness‐to‐pay for quality but also in their reservation utility for the basic product. We find that while the firm offers lower‐quality products when consumers' valuations for quality deteriorate, the optimal quality may increase with a negative shift in consumers' reservation utilities. We also investigate the optimal price and quality of the products within a vertically differentiated product line when the number of products is exogenously given. The existing literature shows that when consumers differ only in their willingness‐to‐pay for quality, the firm sets the efficient quality for consumers with the highest valuation for quality, whereas the concern for cannibalization pushes down the quality of inferior products. We find that when consumers are heterogeneous in both their reservation utility and valuation for quality, the concern for cannibalization may distort the quality upwards, even for consumers with the highest willingness‐to‐pay for quality. In addition, a low‐quality product may enjoy a higher profit margin than a high‐quality product within the product line.     

核事故早期应急群决策模型研究

有效快速的核事故早期应急决策,是核电站发生核事故后最后一道必要的屏障,因此决策的快速性与有效性至关重要。文章先构造效用函数,求出决策者的乐观系数,将决策判断矩阵中的区间值与模糊值精确化;在此基础上建立了个体与群体的决策模型,以提高决策的有效性。同时根据排序结果,构造群体与个体之间一致性判断矩阵,并根据判断矩阵进行交互与修改,使专家内部快速达成一致。最后通过算例说明方法的可行性。     

农户金融需求行为及其影响因素的实证研究

随着改革开放的发展和农民生活水平的提高,农户对金融的需求愈加强烈。基于沈阳周边农户的300份调查问卷,运用世代交叠模型模拟农户经济行为,建立二元Logit模型,对影响沈阳农户金融需求效用的因素进行实证分析。指出农户的家庭收入、经营状况、固定资产、土地、贷款金额和城镇经济状况等因素都对农户金融需求效用存在显著影响,并提出了促进沈阳周边农村金融发展的政策建议,旨为沈阳地区农村经济发展提供借鉴。     

战备物资合同储备合谋防范策略研究

战备物资委托企业合同储备过程中存在多重委托代理关系,结合博弈理论,分析军方-军代表-代储企业三方损益,考虑合谋惩罚因素和名誉损失惩罚因素。在分析合谋形成条件的基础上,建立战备物资合同储备预防合谋机制模型,得出混合战略均衡解,模型的均衡解反映了代储企业与军代表选择违规获取合谋收益的最佳概率,以及军方监管机构选择监督的均衡概率,得出监管力度和监管成本的合理组合,实现监管效益最大化。通过实例仿真讨论模型在不同参数下的合谋条件,识别合谋监管的关键变量,为完善战备物资合同储备监管机制提供参考。     

Configuration of flexibility strategies under supply uncertainty

In this paper, we study a buyer׳s configuration of flexibility strategies under supply uncertainty. His main supplier׳s production process is uncertain, and he can either choose pricing flexibility (setting prices depending on the available supply) or operational flexibility (requesting a contingent order from a backup supplier). As the buyer may or may not find a suitable contingent supplier ex post, we study two scenarios that the backup supplier׳s supply is infinite, and that this supply is random. We also include the factor that the main supplier may determine the wholesale price. We demonstrate that the adoption of flexibility strategies is controlled by threshold policies in different scenarios whether the main supplier determines the wholesale price or not. We also investigate how the buyer׳s attribute (finding a suitable contingent supplier) affects the configuration of flexibility strategies.     

Generalized Estimation of the BLUP in Mixed-Effects Models: A Comparison with ML and REML

The Best Linear Unbiased Predictor (BLUP) in mixed models is a function of the variance components and they are estimated using maximum likelihood (ML) or restricted ML methods. Nonconvergence of BLUP would occur due to a drawback of the standard likelihood-based approaches. In such situations, ML and REML either do not provide any BLUPs or all become equal. To overcome this drawback, we provide a generalized estimate (GE) of BLUP that does not suffer from the problem of negative or zero variance components, and compare its performance against the ML and REML estimates of BLUP. Simulated and published data are used to compare BLUP.     

A Bivariate Distribution Family with Specified Correlation Coefficient and Given Marginals

For given continuous distribution functions F(x) and G(y) and a Pearson correlation coefficient ρ, an algorithm is provided to construct a sequence of continuous bivariate distributions with marginals equal to F(x) and G(y) and the corresponding correlation coefficient converges to ρ. The algorithm can be easily implemented using S-Plus or R. Applications are given to generate bivariate random variables with marginals including Gamma, Beta, Weibull, and uniform distributions.     

简论王国维美学的现代性

站在近代这样的时代峰颠上 ,王国维作为近代著名的学者 ,在他的学术中已经透露出了现代的气息。在美学思想上 ,王国维一反中国传统的“功用”主义思想观 ,提出了他著名的“非功利”美学观念。在王国维看来 ,艺术是超功利的 ,具有其独立的价值和地位。这无疑提高了艺术的地位 ,为日后中国建立独立的艺术精神提供了先验 ;在美学术语上 ,王国维由传统术语经由阐释而转为现代性和由西方引入美学术语这两条途径 ,提出大量的现代美学术语 ,并且在他的文章中加以应用 ,这不能不说是现代性的一个表现。总之 ,王国维为中国美学的现代化作出了卓越的贡献 ,值得后人加以借鉴和研究。