Pooling multivariate data under W, LR and LM tests

Two independent random samples are drawn from two multivariate normal populations with mean vectors μ1 and μ2 and a common variance-covariance matrix Σ. Ahmed and Saleh (1990) considered preliminary test maximum likelihood estimator (PMLTE) for estimating μ1 based on the Hotelling's T _N ², when it is suspected that μ1=μ2. In this paper, the PTMLE based on the Wald (W), Likelihood Ratio (LR) and Lagrangian Multiplier (LM) tests are considered. Using the quadratic risk function, the conditions of superiority of the proposed estimator for departure parameter are derived. A max-min rule for the size of the preliminary test of significance is presented. It is demonstrated that the PTMLE based on W test produces the highest minimum guaranteed efficiencies compared to UMLE among the three test procedures.     

Development of an Attitudes Measure for Prenatal Screening in Diverse Populations

Background: Prenatal screening for chromosomalabnormalities is routinely offered to allpregnant women who present for care by their20th gestational week. Not all women,however, choose to undergo one of these tests,and choice of which test(s) to undergo alsovary. The reasons for variation in screeningtest behavior have not been fully explored.Methods: We examined the psychometricproperties of scales developed to measurefactors related to prenatal screening usingdata collected as part of a survey of 448racial/ethnically diverse pregnant women. These women were consecutively recruited fromprenatal care clinics when they were betweentheir 12th and 20th week ofpregnancy. The Theory of Reasoned Action wasused to develop to measures of attitudes towardand beliefs about prenatal screening. All itemswere subjected to factor analysis. Scalesidentified in the factor analysis were thensubjected to reliability analysis. Allanalysis was conducted for the entire studygroup as well as separately for eachracial/ethnic group.Results: Six scales emerged: who makes medicaldecisions, fatalism, health care trust, valueof screening, fear of screening and value ofpregnancy. All scales had adequate reliabilitywhen the analysis was conducted for the entirestudy group; however there were differences inreliability across racial/ethnic group.Conclusions: Because of these between groupdifferences comparisons of racial/ethnic groupmay be difficult to interpret and potentiallylead to erroneous conclusions.     

Characteristics of U.S. cities with extreme (high or low) crime rates: Results of discriminant analyses of 1960, 1970, and 1980 data

Why do some cities have higher or lower crime rates than others? In this study we attempt to answer this fundamental question by identifying the theoretically motivated structural covariates which differentiate U.S. cities with extreme high and low crime rates. We apply discriminant function analysis across comprehensive samples of all U.S. cities with populations of greater than 25 000 in the periods 1960, 1970, and 1980 and then posit four question: are empirical findings from regression-based studies of city crime rates replicated in discriminant studies with extreme rates? Are the covariates that predict high or low crime rates unique to specific time periods? Which covariates are better able to discriminate high or low rates for specific crimes? And are specific covariates distinguishable in crime rate changes across time periods? Among our general findings, it appears that those cities with extreme high (low) crime rates tend to be the largest (smallest), most (least) economically deprived, and most (least) socially disintegrated. Associations with these latter two characteristics appear to have grown stronger over the past three census periods. The theoretical importance of these and other findings uncovered here are discussed and interpreted through Wilson's (1987) notion of concentration effects and social isolation which may have transformed inner-city areas in recent years.     

Peer influence and drug use among adolescents in rural areas

A sample of 1,004 eighth and tenth grade students in twenty-three small Central/East Texas communities was assessed to determine 1) their perception of the number of their friends who use drugs, 2) the amount of information they received about drugs from their friends, and 3) the connection between those perceptions and drug use. A multiple regression model which included grade, gender, the degree to which friends are perceived to use drugs and the amount of information about drugs received from friends explained 39 percent of the variance in the degree to which rural adolescents were involved in drug use. An item specific analysis of the subcomponents of these composite variables explained 44 percent of the variance in the degree to which rural adolescents were involved in drug use. This same four-factor model accurately classified over 81 percent of non-drug-users and 67 percent of users using discriminant analysis. Students who perceived a higher degree of drug use among their friends and who received more information about drugs from their friends used drugs more frequently. Lower marijuana use in these rural areas as compared to the nation, both as a peer perception and as a fact, may protect these students to a degree from broader patterns of drug use. The findings of this study support the theory that peer pressure is related to drug abuse, even in rural areas.     

The preservation of multivariate comparative statics in nonexpected utility theory

This article investigates the preservation of multivariate expected utility comparative statics for “smooth” nonexpected utility representations. Specifically, we answer the following question: if an expected utility comparative statics property depends only on preferences over sure prospects, then when will a nonexpected utility maximizer with identical sure preferences also satisfy that property? We demonstrate that the effects of increased risk aversion are preserved under the “Almost Degenerate Independence” axiom, but that those of distribution changes of exogenous risks are not preserved under stringent assumptions. Hence, nonexpected utility comparative statics may diverge from expected utility, even for “first-order” properties—those whose effect is determinable from restrictions on “local” utility functions.     

关于土族民间信仰及习惯法的人类学分析

土族习惯法的产生、发展和运作深受土族民间信仰的影响,习惯法中的大部分内容都是由民间信仰中的各种禁忌、仪式、巫术构成,而神灵观念和内心的信仰是土族习惯法最主要的来源,各种禁忌、巫术直接推动着土族习惯法的有效执行。同时,土族习惯法又维系着民间信仰的内在结构,强化了民间信仰的社会功能。     

“I Don't Go By Sean Patrick”: On-Line/Off-Line/Out Identity and SeanPatrickLive.com

Web cams are cameras that are attached to a computer in order to send continuously updated pictures over the Internet. SeanPatrickLive is a Web cam site that documented the life of Sean, a gay man living in the Washington, D.C. area. This essay is the result of ethnographic interviews with Sean Patrick. It discusses Web cams within the context of the cyberqueer, examining how sexuality is presented on-line, using the Internet and the Web cam as a form of gay/queer politics, and performing identity on- and off-line.     

Competitive analysis for make-to-order scheduling with reliable lead time quotation

This paper makes extended studies on the discrete problem of online scheduling and reliable lead time quotation (discrete Q-SLTQ) introduced by Keskinocak et al. (Manag. Sci. 47(2):264–279, 2001). We first relax the assumption on revenue function from a linear decreasing function to any decreasing function. We present an online deterministic strategy which is optimal in competitiveness for concave revenue functions. The above results are further extended to the continuous Q-SLTQ model where orders are released at arbitrary time points. For the discrete Q-SLTQ problem, if orders are with nonuniform lengths, we prove the nonexistence of online strategies with bounded competitive ratios; otherwise if orders are with unit length but various weights, we present an optimal online strategy.