Assessing the Potential Impact of the HIV-1 Epidemic on Orphanhood and the Demographic Structure of Populations in sub-Saharan Africa

Much of the debate on the demographic consequences of the HIV epidemic in sub-Saharan Africa has so far centred around the plausibility of population declines in areas where unprecendently high rates of population growth have recently been in evidence. In this article, the authors use a mathematical model, which combines epidemiological and demographic processes, to illustrate how, under a broad range of impacts on population growth, major changes in demographic features, such as the extent of orphanhood within populations, are likely to occur. At the same time, HIV epidemics are liable to cause significant shifts in the age and sex composition of affected populations, which may have important implications for the ways in which they are best able to cope with the increases in orphanhood, as well as those in infant, early childhood and adult mortality.     

Finite mixtures of multivariate skew t-distributions: some recent and new results

Finite mixtures of multivariate skew t (MST) distributions have proven to be useful in modelling heterogeneous data with asymmetric and heavy tail behaviour. Recently, they have been exploited as an effective tool for modelling flow cytometric data. A number of algorithms for the computation of the maximum likelihood (ML) estimates for the model parameters of mixtures of MST distributions have been put forward in recent years. These implementations use various characterizations of the MST distribution, which are similar but not identical. While exact implementation of the expectation-maximization (EM) algorithm can be achieved for ‘restricted’ characterizations of the component skew t-distributions, Monte Carlo (MC) methods have been used to fit the ‘unrestricted’ models. In this paper, we review several recent fitting algorithms for finite mixtures of multivariate skew t-distributions, at the same time clarifying some of the connections between the various existing proposals. In particular, recent results have shown that the EM algorithm can be implemented exactly for faster computation of ML estimates for mixtures with unrestricted MST components. The gain in computational time is effected by noting that the semi-infinite integrals on the E-step of the EM algorithm can be put in the form of moments of the truncated multivariate non-central t-distribution, similar to the restricted case, which subsequently can be expressed in terms of the non-truncated form of the central t-distribution function for which fast algorithms are available. We present comparisons to illustrate the relative performance of the restricted and unrestricted models, and demonstrate the usefulness of the recently proposed methodology for the unrestricted MST mixture, by some applications to three real datasets.     

Age discrimination and working life: Perspectives and contestations – a review of the contemporary literature

This review highlights some of the principal issues and debates surrounding age discrimination at the workplace. Essentially, the existing research in this area can be divided into three broad, although somewhat overlapping, categories. The first explores the underlying causes and consequences of age discrimination at the workplace from one or other theoretical tradition. The second broad body of literature encompasses empirical studies which document the nature and extent of age discrimination, based on the use of official statistics, and/or firm‐level survey evidence. The third explores the effects of various governmental initiatives to reduce the incidence of age discrimination and policy options in this area. Even though age discrimination is widely accepted to be prevalent, its causes are rather more contentious. Age discrimination has variously been ascribed to market imperfections, the product of rational choices and the effects of long‐term changes in the nature of the economy. Policy interventions may be prompted by economic pressure, demographic changes or cultural shifts, and have involved voluntary codes as well as legislation. Although voluntary codes have generally proved ineffective, the literature indicates that more formal regulations may still have only limited efficacy, underscoring the deeply rooted nature of age discrimination in society.     

The Siable-Law Model of Stock Returns

This study investigates the tail shapes of empirical distributions of returns on an extensive group of common stocks. The tails of the return distributions are found to be thinner than those of infinite variance stable distributions. Therefore, although homogeneity is evident in general, economic and statistical inferences drawn from stable-law parameters estimated from samples of stock returns may be misleading. This is in spite of the apparent overall similarity (in shape) between empirical and stable distributions.     

卫藏方言与安多方言语音分析

安多方言和卫藏方言虽属藏语两大不同的方言区,但在一种超方言的文字统一的情况下,两者之间的区别及联系在汉藏语系里虽非绝无仅有,也是异常罕见的.从卫藏和安多方言的发音入手,通过语音分析、比较,对安多人学习卫藏方言的方法进行探讨,将有助于两大语言区人们间的沟通与交流.     

SHORT REVIEWS

Books reviewed in this article: Orley Ashenfelter And David Card (Eds.), Handbook of Labor Economics, Volume 3 Paul Boyle, Keith Halfacree, and Vaughan Robinson, Exploring Contemporary Migration Weixing Chen, The Political Economy of Rural Development in China, 1978–1999 David A. Crocker and Toby Linden (Eds.), Ethics of Consumption: The Good Life, Justice, and Global Stewardship James Z. Lee and Wang Feng, One Quarter of Humanity: Malthusian Mythology and Chinese Realities, 1700–2000 Jonathan M. Mann and Daniel J. M. Tarantola (Eds.), AIDS in the World II: Global Dimensions, Social Roots, and Responses Julian L. Simon, The Economic Consequences of Immigration, Second Edition Sopemi, Trends in International Migration: Continuous Reporting System on Migration. Annual Report, 1999 Edition Jacqueline Stevens, Reproducing the State United Nations Development Programme China, The China Human Development Report United Nations, Economic Commission For Europe, Economic Survey of Europe 1999, No. 1 Kathleen S. Uno, Passages to Modernity: Motherhood, Childhood, and Social Reform in Early Twentieth Century Japan     

Inventory management and cost-benefit analysis: A case study

This paper treats the problem of comparing various stocking and issuing policies for two radioactive isotopes, I-123 and I-131, which are used in nuclear medicine departments for the diagnosis of thyroid disease. The approach is based on using a combination of a cost-benefit analysis to compare the increased operating costs of stocking I-123 versus the increased disease risk of using I-131, and simulation to recreate the operation of a radio-pharmacy which stocks these drugs. The required inputs to the model include: (1) estimates of the disease risks associated with radiation absorbed doses from I-131; (2) estimates of the probability distributions of the appropriate latent periods; (3) empirical distributions of daily patient demand; (4) census data for estimating longevity and individual expected earnings and (5) cost data the stocking costs of the isotopes. The cost benefit results give issuing rules based on the age and sex of the patient, while the simulation is used to compare the effectiveness of the various ordering policies considered (the choice of a particular ordering policy may influence the risk of disease development).