Improved minimax estimation of a normal precision matrix

Let S_{p × p} have a Wishart distribution with parameter matrix Σ and n degrees of freedom. We consider here the problem of estimating the precision matrix Σ^?1 under the loss functions L₁(σ) tr (σ) - log |σ| and L₂(σ) = tr (σ). James-Stein-type estimators have been derived for an arbitrary p. We also obtain an orthogonal invariant and a diagonal invariant minimax estimator under both loss functions. A Monte-Carlo simulation study indicates that the risk improvement of the orthogonal invariant estimators over the James-Stein type estimators, the Haff (1979) estimator, and the “testimator” given by Sinha and Ghosh (1987) is substantial.     

Challenging the Rhetoric of Choice in Maternal Labour‐Force Participation: Preferred Versus Contracted Work Hours

The notion of choice in maternal labour‐force participation (LFP) is a contentious one, with assertions that LFP is a direct result of either personal inclinations, such as employment commitment or external factors, such as historically available opportunities. This article suggests an alternative framework for understanding and testing choice in LFP using preferred versus contracted work hours. It explores these constructs quantitatively in a group of working mothers (N = 275) with dependent children and investigates qualitatively the underlying reasons for discrepant preferred versus contracted work hours in a sub‐sample of these women with under‐school‐aged children (N = 20). The results show that nearly two‐thirds of women working full time would prefer to work part time and the major reasons for not acting on their preferences is because of the nature of the job and the lack of career opportunities available for part‐time employees.     

Understanding Social Change in Conducting Research on Adolescence

In the present essay, we focus on G. Stanley Hall's contributions to the study of the role of social change for adolescent development. After introducing Hall's main ideas, we discuss recent demands adolescents face because of social change and how Hall's work could inform research on adolescent development in times of social change.     

Temporal Aggregation of Stationary and Non-stationary Continuous-Time Processes

Abstract.  We study the autocorrelation structure of aggregates from a continuous-time process. The underlying continuous-time process or some of its higher derivative is assumed to be a stationary continuous-time auto-regressive fractionally integrated moving-average (CARFIMA) process with Hurst parameter H . We derive closed-form expressions for the limiting autocorrelation function and the normalized spectral density of the aggregates, as the extent of aggregation increases to infinity. The limiting model of the aggregates, after appropriate number of differencing, is shown to be some functional of the standard fractional Brownian motion with the same Hurst parameter of the continuous-time process from which the aggregates are measured. These results are then used to assess the loss of forecasting efficiency due to aggregation.     

第6章新官上任

《龟航》是一部职场小说, 同时也是一部代表了特定人群的小说,在这个大时代下,境遇变迁,冲击着每一个人。海归的遭遇更能折射出现实的意义。本刊现独家连载这部原创作品。您从作者清新幽默的文笔下读到的将是新世纪《围城》的深刻和感同身受。     

挑战人生

《龟航》是一部职场小说, 同时也是一部代表了特定人群的小说,在这个大时代下,境遇变迁,冲击着每一个人。海归的遭遇更能折射出现实的意义。本刊现独家连载这部原创作品。您从作者清新幽默的文笔下读到的将是新世纪《围城》的深刻和感同身受。     

Venture philanthropy and social entrepreneurship in community redevelopment

This article provides a case study of Tom Cousins, a social entrepreneur who used his own venture philanthropic investments and leveraged additional resources through extensive public‐private partnerships for the sole intent of redeveloping an area of disinvestment and poverty. In the process, Cousins also provided the visionary, strategic, and operational leadership often associated with the actions and responsibilities of a social entrepreneur. The limited research to date has investigated social entrepreneurship and venture philanthropy as separate and often unrelated concepts. In this study, we analyze the sustained and intensive involvement by Cousins and his foundations and the continued leadership provided in the creation of public‐private partnerships focused on the redevelopment of the East Lake area in Atlanta.