Analysis of overdispersed paired count data

This article is about the statistical analysis of overdispersed paired count data for comparing two treatments. The data consist of the number of events obtained in a stratum during the fixed observation period. Three types of model are discussed: the Poisson, a mixed, and a semiparametric model. Overdispersion is represented in the last two models but not in the Poisson model. Of particular interests are to examine whether there is any loss of efficiency in using the estimate of the treatment effect obtained under other two models if the mixed model is true, and also whether overdispersion leads to a larger variance of the estimate than that expected from the Poisson model. It is shown that all three models provide the same estimate of the treatment effect (i.e., there is no loss of efficiency) and that the variance of the estimate of the treatment effect obtained under the Poisson model is the same as that based on the mixed model. However, the semiparametric model provides the variance of the estimate larger than those obtained under the other two models.     

The probability of degenerate maximum-likelihood estimates with randomly truncated survival data

We study the nonparametric maximum-likelihood estimator of the marginal distribution function in bivariate data with truncated sum (Woodroofe 1985), and calculate the probability that it will assign zero probability to a range of observed values. We show that in a simple artificial model with uniform intensity in both variables the probability may be expressed using recursive formulae, and that large-sample approximations valid under weak regularity conditions show good agreement with as few as 20 observations. In the uniform-intensity model, the probability of degenerate estimates is rather small, being just over 5% with a dataset of 20 observations and falling below 1% with 125 observations. However, in a model of transfusion-associated AIDS in 125 children and adults (Kalbfleisch and Lawless 1989), the probability of degenerate estimates is much larger—about 30% with 20 observations and 3% with the actual 125 observations. This is largely because both the infection and incubation density are increasing over time. Such a pattern makes the condition for degeneracy, i.e., relatively high observed intensity at extreme values of each variable, much more likely.     

A Flexible Evaluative Framework for Order Picking Systems

This paper develops a novel framework to evaluate the integral performance of order picking systems with different combinations of storage and order picking policies. The warehousing literature on order picking mostly considers minimizing either elapsed time or distance as the sole objective, whereas warehouse managers in a supply chain have to look beyond single‐dimensional performance and consider trade‐offs among different criteria. Thus managers still need a unified and efficient framework to select a portfolio of appropriate order picking policies from a multi‐criteria and contextual perspective. Our framework—combining data envelopment analysis, ranking and selection, and multiple comparisons—provides an efficient methodology to simultaneously analyze several interrelated problems in order picking systems with multiple performance attributes, such as service levels and operational costs. We demonstrate our approach through comprehensive evaluations of order picking policies in three low‐level, picker‐to‐parts rectangular warehouses facing demand variations.     

物资调运时间为区间数的最短路问题研究

针对紧急状态下物资调配时间为区间数问题,在经典的Dijkstra算法基础上,通过定义一个算子,把区间数序关系转换成实数序关系,对区间数进行排序,给出了区间数的最短路算法。     

移动数据业务国际漫游与互通

本文通过研究移动数据业务国际漫游与互通情况,分析了目前已经投入商用的SMS和MMS数据业务的国际漫游与互通方案,最后提出了从移动通信国际标准合作、运营商之间合作、用户使用等三个方面来解决移动数据业务国际漫游与互通问题。     

Binary Response Models for Panel Data: Identification and Information

This paper considers a panel data model for predicting a binary outcome. The conditional probability of a positive response is obtained by evaluating a given distribution function (F) at a linear combination of the predictor variables. One of the predictor variables is unobserved. It is a random effect that varies across individuals but is constant over time. The semiparametric aspect is that the conditional distribution of the random effect, given the predictor variables, is unrestricted. This paper has two results. If the support of the observed predictor variables is bounded, then identification is possible only in the logistic case. Even if the support is unbounded, so that (from Manski (1987)) identification holds quite generally, the information bound is zero unless F is logistic. Hence consistent estimation at the standard pn rate is possible only in the logistic case.     

Non‐dominated Time‐Window Policies in City Distribution

Urban freight contributes significantly to pollution, noise disturbance, traffic congestion, and safety problems in city centers. In many cities, local governments have introduced policy measures, in particular time‐access restrictions, to alleviate these problems. However, setting time windows is very challenging due to the conflicting interests and objectives of the stakeholders involved. In this article, we examine whether it is possible to develop time‐window policies that enhance environmental sustainability and distribution efficiencies, while meeting the objectives of the municipalities. We develop a framework for balancing retailer (costs), municipality (satisfaction), and environmental (emissions) objectives, using data envelopment analysis, under different urban time‐window policies. The approach is illustrated by a case study of three Dutch retail organizations, with a large number of stores affected by such time windows. On the basis of an evaluation of 99 different time‐window policies, our results show that harmonizing time windows between neighboring cities leads to the best overall performance. The currently used time‐window policy appears to perform reasonably well, but can be improved on all dimensions . However, harmonizing time‐window policies may be difficult to realize in practice.     

Third-grade retention and reading achievement in Texas: A nine year panel study

The academic performance of over 38,000 Texas students who failed the state’s 1994 reading test was examined through their sophomore year in high school. Propensity score matching resulted in strata with retained and promoted students of comparable observed characteristics. Reading scores were analyzed using a two-level hierarchical linear model. Same grade comparisons show that third graders failing the state-mandated reading test who repeated the grade consistently outperformed in later grades the socially promoted children who also failed the third grade test. Additional analyses indicate that alternative explanations for the findings such as omitted variables, regression to the mean, differential panel attrition and cohort effects are not supported. The results are consistent with findings from other recent studies which suggest that grade retention in third grade may help increase student achievement.     

浅析大数据背景下网络营销服务模式的革新

"大数据"技术具有着极高的科技价值和经济价值,基于大数据的网络营销已经成为企业智慧营销的重要手段。本文先从商务和技术两个角度分析了大数据技术的内涵,然后分析了大数据技术在网络营销领域的应用,最后提出企业在应用大数据技术过程中应该注意的问题,以期促进大数据技术在网络营销领域的应用和发展。     

从《史记·五帝本纪》看司马迁的学术研究方法

《五帝本纪》作为《史记》开篇之作,被誉为“中华正史第一本纪”,历来受到学界广泛的关注和高度评价.《史记·五帝本纪》体现出司马迁的“实录”精神和学术研究方法,主要体现为资料收集的广博性、田野调查的广泛性、甄别选材的严谨性、研究思考的深入性等方面.司马迁的“实录”精神和学术研究方法不仅是对历史事实的秉笔直书,更是严谨求实的科学研究方法的体现,对于当今学术研究仍具有深刻的启示作用.