Snapshot samples

We consider a coverage model where an initial event that occurs at some point in time triggers an activity of random duration that leads to some subsequent event. A snapshot sample is constructed at a fixed point in chronological time either by sampling only subjects where the initial event has occurred but the subsequent event has yet to occur (active subjects), or by sampling only subjects where both the initial and subsequent events have occurred (inactive subjects). The biases inherent in snapshot sampling can be neatly characterized by the properties of two random variables: the history (defined as the time the initial event occurs as measured into the past from the chronological point of sampling), and the active time (defined as the length of time between the initial and subsequent events). Though snapshot samples are biased, recognizing the biases enables correct inferences to be drawn from snapshot-sampled data. Considering only the case where and are independent random variables, this paper presents the probability models associated with snapshot sampling, demonstrates the problems that can occur, offers procedures for overcoming these problems, and applies the methods to interesting data sets.     

Web服务:颠覆性的创造力

Gartner观点:Gartner的专家们认为直至2003年Web服务才能真正发展起来。2003年全球40%的电子商务贸易将利用Web服务来完成,2004年这一数字将超过50%,而交易时间将大大缩短。2003年大约80%的开发平台将支持Web服务体系,Web服务将代表下一代软件开发平台的发展方向。据调查显示,在创建Web服务应用程序时,有78%的人使用的是J2EE,并且认为它是最有效的创建和配置Web服务的平台;而使用微软.Net的人为22%。从中我们似乎可以看出哪一个平台更适合于Web服务,哪一个平台又更适合于大多数的开发者。这两个平台的竞争,在2002年愈演愈烈。     

Optimal Generic Advertising with a Rationed Related Good: The Case of Canadian Beef and Chicken Markets

An optimal advertising rule is derived for a good sold in an open market (beef) when a related substitute good (chicken) is production rationed and whose imports are subject to trade restrictions. Such a rule is developed using a multi-market equilibrium displacement model that reflects demand interrelatedness, open trade of the advertised good (beef), with rationed production and restricted trade of the related good (chicken). The optimal rule nests earlier optimal advertising rules under a variety of conditions. Results underscore the importance of accounting for cross-product advertising effects. When these effects are present (absent), the optimal generic beef advertising intensity in Canada is shown to fall (rise) with elimination of supply management in Canada's chicken sector.
L'auteur dérive une règie sur l'optimisation de la publicité pour un produit vendu sur un marché libre (bœuf) en présence d'un produit de substitution rationné dont on restreint les importations. Pour parvenir à une telle règie, l'auteur a utilisé un modèle de déplacement du point d'équilibre sur un marché multiple illustrant les liens entre la demande des produits concernés, le libre-échange du produit faisant l'objet de la publicité (bœuf) et la restriction de la production et des importations du produit apparenté (poulet). La règie d'optimisation englobe les règles antérieures sur l'optimisation de la publicité dans diverses situations. Les résultats soulignent qu'il est important de prendre en compte les retombées de la publicité sur les autres produits. Au Canada, en présence (absence) de telles retombées, le degré optimal de publicité générique sur le bœuf diminue (augmente) avec l'abolition de la gestion de l'offre de poulet.     

The Dynamics of Alliance Conditions in the Alliance Development Process

One of the key issues in understanding the developmental processes of strategic alliances is how the alliance conditions change over the different stages of alliance development. A related question concerns the nature of the co-evolutionary dynamics of alliances in terms of their constituent partner firms. In this article we propose an integrated process model of alliances that is based on alliance conditions, allianc developmental stages, and an alliance system comprising co-evolutionary elements. We suggest that alliance conditions, or the key characteristics of an alliance at any given moment, link the alliance environment (firm characteristics) and the alliance development process. We also explore how specific patterns of alliance conditions have differential impacts on the interactive elements of the alliance co-evolutionary system.     

On the E-optimality of truncated block designs

Sufficient conditions are found for designs, derived from completely symmetric designs by deleting binary blocks, to be E-optimal. Sufficient conditions are also found for E-optimality of designs obtained from other E-optimal designs by deleting all blocks forming a balanced incomplete block design on a subset of the treatments. The results include many binary and non-binary designs for which E-optimality was previously unknown.     

School Choice and the Distributional Effects of Ability Tracking: Does Separation Increase Inequality?

Tracking programs have been criticized on the grounds that they harm disadvantaged children. The bulk of empirical research supports this view, but existing studies compare outcomes across students placed in different tracks. Track placement is likely to be endogenous with respect to student outcomes. We use a new strategy for overcoming the endogeneity of track placement and find no evidence that tracking hurts low-ability children. Previous studies have also been based on the assumption that students' enrollment decisions are unrelated to whether or not the school tracks. When we account for the possibility that tracking programs affect school choice, we find evidence that they may help low-ability children.     

Assessing academic department efficiency at a public university

The assessment of public universities has gained importance because of the demands from such state government bodies as the executive and the legislature. Public universities are increasingly being asked to account for how efficiently they have used diminishing state financial resources. Administrators thus have the responsibility of ensuring that the university's financial, human, and physical resources are allocated to academic departments in a manner that enhances the institution's efficiency. In this paper, data envelopment analysis (DEA) is proposed for evaluating the efficiency of academic departments at a public university. DEA provides a single measure of efficiency for each academic unit. It also identifies the causes behind the inefficiencies exhibited by poor performing units, as well as the changes that these units need to make in order to improve their efficiencies. Its usefulness as a planning tool is also discussed. Copyright © 2002 John Wiley & Sons, Ltd.