A Multiple-community Overlap Measure Based on a Probabilistic Approach

Species diversity indices are designed to measure the species diversity of a community and to compare the species distribution structure of two communities. The Shannon and Simpson indices are for describing one community, and the Jaccard and Morisita indices are for comparing two communities. Only a few indices allow the simultaneous comparison of three or more communities. In this study, we propose a multiple-community similarity index based on a probabilistic approach, and compare it with other multiple-community indices. Empirical examples are considered as a demonstration of the proposed similarity indices.     

A Simplified Treatment of the Estimation of Parameters and Tests of Hypotheses in Constrained Design Models with Unbalanced Data

A simple approach to the least squares estimation of parameters in the linear design model is given. An algebraically tractable example for unbalanced data is used to illustrate the approach.     

在中国科技大学的日子

1991年,我和我的妻子Alison第一次来到中国,开始了一段不平凡的经历。初次踏上这片遥远的、极具异国情调的土地,兴奋中更多的却是陌生。然而,十几年过去,我们已经逐渐适应并越来越热爱这里的生活与工作。我应聘的单位是中国科学技术大学,主要工作是指导博士生如何用英语来展示他们的科研成果,这是一项非常有意义的工作,能够经常接触到科研领域中许多令人着迷的最新成果。来中国之前,我一直在加拿大的滑铁卢大学教授计算机科学课程,每每想到因指导博士生而不能对自己从事的科研领域投入太多的时间,总会有一丝淡淡的怅惘涌上心头。然而,每当…     

A dynamic EM algorithm for estimating mixture proportions

We investigate the use of a dynamic form of the EM algorithm to estimate proportions in finite mixtures of known distributions. We prove a consistency result for this algorithm, which employs only a single EM update for each new observation. Our aim is to demonstrate that the slow convergence rate of the EM algorithm in many applications is of little practical consequence in a situation when data is frequently being updated.     

Residential Air Exchange Rates in the United States: Empirical and Estimated Parametric Distributions by Season and Climatic Region

The purpose of this paper is to undertake a statistical analysis to specify empirical distributions and to estimate univariate parametric probability distributions for air exchange rates for residential structures in the United States. To achieve this goal, we used data compiled by the Brookhaven National Laboratory using a method known as the perfluorocarbon tracer (PFT) technique. While these data are not fully representative of all areas of the country or all housing types, they are judged to be by far the best available. The analysis is characterized by four key points: the use of data for 2,844 households; a four-region breakdown based on heating degree days, a best available measure of climatic factors affecting air exchange rates; estimation of lognormal distributions as well as provision of empirical (frequency) distributions; and provision of these distributions for all of the data, for the data segmented by the four regions, for the data segmented by the four seasons, and for the data segmented by a 16 region by season breakdown. Except in a few cases, primarily for small sample sizes, air exchange rates were found to be well fit by lognormal distributions (adjusted R² 0.95). The empirical or lognormal distributions may be used in indoor air models or as input variables for probabilistic human health risk assessments.     

The mediated innovation model: A framework for researching media influence in language change

Linguistic innovations that arise contemporaneously in highly distant locations, such as quotative be like, have been termed ‘global linguistic variants’. This is not necessarily to suggest fully global usage, but to invoke more general themes of globalisation vis‐à‐vis space and time. This research area has grown steadily in the last twenty years, and by asserting a role for mass media, researchers have departed intrepidly from sociolinguistic convention. Yet they have largely relied on quite conventional sociolinguistic methodologies, only inferring media influence post hoc. This methodological conservatism has been overcome recently, but uncertainty remains about the overall shape of the new epistemological landscape. In this paper, I review existing research on global variants, and propose an epistemological model for researching media influence in language change: the mediated innovation model. I also analyse the way arguments are constructed in existing research, including the use of rhetorical devices to plug empirical gaps – a worthy sociolinguistic topic in its own right.     

Commissioned analysis of surgical performance using routine data: lessons from the Bristol inquiry

The public inquiry into paediatric cardiac surgery at the Bristol Royal Infirmary commissioned the authors to design and conduct analyses of routine data sources to compare surgical outcomes between centres. Such analyses are necessarily complex in this context but were further hampered by the inherent inconsistencies and mediocre quality of the various sources of data. Three levels of analysis of increasing sophistication were carried out. The reasonable consistency of the results arising from different sources of data, together with a number of sensitivity analyses, led us to conclude that there had been excess mortality in Bristol in open heart operations on children under 1 year of age. We consider criticisms of our analysis and discuss the role of statisticians in this inquiry and their contribution to the final report of the inquiry. The potential statistical role in future programmes for monitoring clinical performance is highlighted.