A two-stage procedure for selecting the best of k exponential distributions

The problem of selecting the best of k exponential distributions with different guarantee times and the same unknown variance is considered. A two-stage procedure, similar to the one considered by Bechhofer, Dunnett and Sobel (1954), is given. Some specific guidelines for selecting the first-stage sample size are also given.     

Some results for maximum likelihood estimation of adjusted relative risks

Maximum likelihood (ML) estimation of relative risks via log-binomial regression requires a restricted parameter space. Computation via non linear programming is simple to implement and has high convergence rate. We show that the optimization problem is well posed (convex domain and convex objective) and provide a variance formula along with a methodology for obtaining standard errors and prediction intervals which account for estimates on the boundary of the parameter space. We performed simulations under several scenarios already used in the literature in order to assess the performance of ML and of two other common estimation methods.     

Student homicidal violence in schools: an international problem

School homicides have been become a worldwide phenomenon. In the decade following the Columbine shooting there have been at least forty similar events in other countries. This article addresses the international scope of this problem and some of the complex conceptual issues that make student homicidal violence difficult to define and study. Meaningful research on risk and protective factors that can inform evidence-based preventive models is summarized.     

Estimating Listeria monocytogenes Growth in Ready-to-Eat Chicken Salad Using a Challenge Test for Quantitative Microbial Risk Assessment

Currently, there is a growing preference for convenience food products, such as ready-to-eat (RTE) foods, associated with long refrigerated shelf-lives, not requiring a heat treatment prior to consumption. Because Listeria monocytogenes is able to grow at refrigeration temperatures, inconsistent temperatures during production, distribution, and at consumer's household may allow for the pathogen to thrive, reaching unsafe limits. L. monocytogenes is the causative agent of listeriosis, a rare but severe human illness, with high fatality rates, transmitted almost exclusively by food consumption. With the aim of assessing the quantitative microbial risk of L. monocytogenes in RTE chicken salads, a challenge test was performed. Salads were inoculated with a three-strain mixture of cold-adapted L. monocytogenes and stored at 4, 12, and 16 °C for eight days. Results revealed that the salad was able to support L. monocytogenes’ growth, even at refrigeration temperatures. The Baranyi primary model was fitted to microbiological data to estimate the pathogen's growth kinetic parameters. Temperature effect on the maximum specific growth rate (μ_max) was modeled using a square-root-type model. Storage temperature significantly influenced μ_max of L. monocytogenes (p < 0.05). These predicted growth models for L. monocytogenes were subsequently used to develop a quantitative microbial risk assessment, estimating a median number of 0.00008726 listeriosis cases per year linked to the consumption of these RTE salads. Sensitivity analysis considering different time–temperature scenarios indicated a very low median risk per portion (<−7 log), even if the assessed RTE chicken salad was kept in abuse storage conditions.     

Teaching Communication in a Statistical Collaboration Course: A Feasible,Project-Based,Multimodal Curriculum

Many schools offer a statistical collaboration curriculum using standard instructional methods such as lectures whereby students are taught to successfully apply their training. The process of building statisticians' collaborative skills and characteristics can be challenging due to logistical issues, time constraints, unstructured research problems, and resources. Instructors vary in their pedagogy and topics taught, and students' experiences vary. There is a dearth of literature describing how to implement a course integrating communication skills, critical thinking, collaboration, and the integration of team members in a learner-centered format. Few courses integrate behavior-based learning using role-playing, video demonstration and feedback, case-based teaching activities, and presentation of basic statistical concepts. We have developed and implemented a two-semester biostatistics collaboration course, of which the purpose is to develop the students' knowledge, skills, attitudes, and behaviors necessary to interact effectively with investigators. Our innovative curriculum uses a multimodal, project-based, experiential process to address real-world problems provided by real and/or simulated collaborators while minimizing usual challenges. Rubrics and peer evaluation forms are offered as online supplementary materials. This article describes how a collaboration curriculum focusing on communication and team practice is feasible, how it enhances skill and professionalism, and how it can be implemented at other institutions.     

A Lean transportation approach for improving emergency medical operations

Abstract

This paper extends the approach of Lean transportation to improve the performance of emergency medical processes (EMP) by adapting its main concepts into the main characteristics of the EMP environment. The paper is based on an inductive theory-building process initiated from a case study in the field of emergency medical services. The development of the suggested performance improvement approach triggered from an exhaustive analysis of a process involved and an exploratory review of the existing improvement approaches available. The process of concern can be described as a specialized transportation process, where human lives are at risk. Its characteristics led to a natural application of Lean transportation. The results include, a novel approach for improving the agility and efficient EMS processes. This is validated with an application for improving ambulance response times and turnaround times of the Red Cross operations located in Monterrey, Mexico. The approach proved to be an integrated scheme for identifying waste opportunities at a systems level. This characteristic is important to let operations management prioritize improvement efforts in a limited budget situation. This work suggests the application of the emerging Lean transportation approach for increasing the agility performance of EMS processes.     

Travelling from New Spain to Mexico: Mapping Practices of Nineteenth-Century Mexico

James Horn, Adapting to a New World: English Society in the Seventeenth‐Century Chesapeake (1994), xv + 461 (University of North Carolina Press, Chapel Hill, $60.50).

Marguerite W. Dupree, Family Structure in the Staffordshire Potteries, 1840–1880 (1995), xx + 405 (Clarendon Press, Oxford, £48.00).

David B. Copian, In the Time of Cannibals: The Word Music of South Africa's Basotho Migrants (1994), xxi + 300 (University of Chicago Press, Chicago, $55.00, paperback $18.95).

Ellen Meiksins Wood, Democracy Against Capitalism: Renewing Historical Materialism (1995), 300 (Cambridge University Press, London, £35.00).