Sleep habits and patterns of college students: a preliminary study.

The negative effects of sleep difficulties have been well documented. However, the prevalence of such problems among US college students has not been well studied. Design difficulties are common in the limited number of existing investigations, making it difficult to estimates the prevalence and types of disturbance studied. The authors describe the use of a quantitative-based assessment instrument to provide an initial indication of students' sleep problems and to serve as a means of addressing some of the deficiencies in the literature. In their sample of 191 undergraduates at a rural southern university, they found that most of the students exhibited some form of sleep disturbance and that women, in general, reported more sleep disturbances than men did. They suggest how colleges and university officials can alter procedures to minimize students' sleep disturbances and reduce the deleterious effects of sleep problems on academic performance.     

The Future Challenge for Direct Payments

Since 1997, Local Authorities have had the discretionary power to pay cash directly to disabled adults up to the age of 65 and assessed as needing social service support. More recently, the scope of Direct Payments has been widened to include people aged over 65 years and will, under the Health and Social Care Act 2001, be extended to further groups including disabled people from 16 to 18 years of age and parent carers of young children with impairments. Direct Payments have the potential not only to impact radically upon an individual's quality of life but also to influence the 'community care' market economy and the way personal support services are purchased and delivered in the future. Recent figures from a survey undertaken by the Association of Directors of Social Services suggest that 80% of local authorities have already introduced a Direct Payments scheme and that over 3500 people are already in receipt of direct payments (Jones, 2000). This paper is based upon evidence from a user-controlled Best Value Review of Direct Payments (BVDP) in Wiltshire. It explores, from disabled people's perspective, the advantages and disadvantages of Direct Payments, and demonstrates the challenges still facing both service users and service providers.     

The utility of experimental design short courses?

This paper describes the one‐day introduction to experimental design training course at GlaxoSmithKline. In particular, the use of paper helicopter experiments has been an effective and efficient method for teaching experimental design techniques to scientific and other staff. A good supporting strategy by which the statistics department provides back‐up following the course is essential. Copyright © 2002 John Wiley & Sons, Ltd.     

A Bayesian decision theory approach to variable selection for discrimination

Motivated by examples in spectroscopy, we study variable selection for discrimination in problems with very many predictor variables. Assuming multivariate normal distributions with common variance for the predictor variables within groups, we develop a Bayesian decision theory approach that balances costs for variables against a loss due to classification errors. The approach is computationally intensive, requiring a simulation to approximate the intractable expected loss and a search, using simulated annealing, over a large space of possible subsets of variables. It is illustrated by application to a spectroscopic example with 3 groups, 100 variables, and 71 training cases, where the approach finds subsets of between 5 and 14 variables whose discriminatory power is comparable with that of linear discriminant analysis using principal components derived from the full 100 variables. We study both the evaluation of expected loss and the tuning of the simulated annealing for the example, and conclude that computational effort should be concentrated on the search.     

Logic and Motivation in Risk Research: A Nuclear Waste Test Case

After two decades of massive investigation, federal approval of a nuclear waste site is drawing to a close. Large-scale research to assure that major hazards such as this one are socially acceptable is often highly inefficient, as here. A regulatory remedy would be to require not only that risk currently assessed be acceptable, but also that risk would remain acceptable given any new information. Research to test compliance with these rules has to be cost effective. Research activities should be managed according to an explicit discipline that can be imposed on powerful conflicting interests. They might be required to (1) set targets for the first- and second-order risk assessments, (2) allocate research resources to close any gap between current and target assessments cost effectively, and (3) reallocate resources, as evolving findings dictate. The interests of license applicant (Department of Energy, DOE) and society are distinguished: the former would want the application approved; the latter would want to reject an unacceptable facility.     

Debt and Financial Expectations: An Individual- and Household-Level Analysis

In this article we show that optimistic financial expectations impact positively on both the quantity of debt and the growth in debt at the individual and household levels. Our theoretical model shows that this association is predicted under a variety of plausible scenarios. In the empirical analysis we explore the determinants of debt and of growth in debt using British data. We find convincing support for our theoretical priors and show that it is optimistic financial expectations per se that are important in influencing debt, rather than the accuracy of individuals' predictions regarding their future financial situation.     

Reducing disablement with adequate and appropriate resources: a New Zealand perspective

This article presents the qualitative findings from a larger mixed methods study of the barriers and costs associated with disability in New Zealand. A social model of disability framework was integrated with an economic cost model using consensual budget standards to (1) identify key barriers disabled people experience in their everyday living and (2) develop consensus about the resources disabled people agree they require to reduce or remove them. Forty-nine people with physical, hearing, vision or intellectual impairment participated in a series of 8 impairment-based focus groups. The analysis identified inaccessible environments, negative attitudes, unreliable transportation and poor access to information as key barriers. However, lack of adequate and appropriate resources (e.g. equipment, modifications, support, transport and time) to address these barriers was the overarching obstacle to participation. The inclusion of time as both a barrier and a valuable resource is arguably the most important contribution of the study.     

A statistical method for synthesizing mediation analyses using the product of coefficient approach across multiple trials

Mediation analysis often requires larger sample sizes than main effect analysis to achieve the same statistical power. Combining results across similar trials may be the only practical option for increasing statistical power for mediation analysis in some situations. In this paper, we propose a method to estimate: (1) marginal means for mediation path a, the relation of the independent variable to the mediator; (2) marginal means for path b, the relation of the mediator to the outcome, across multiple trials; and (3) the between-trial level variance–covariance matrix based on a bivariate normal distribution. We present the statistical theory and an R computer program to combine regression coefficients from multiple trials to estimate a combined mediated effect and confidence interval under a random effects model. Values of coefficients a and b, along with their standard errors from each trial are the input for the method. This marginal likelihood based approach with Monte Carlo confidence intervals provides more accurate inference than the standard meta-analytic approach. We discuss computational issues, apply the method to two real-data examples and make recommendations for the use of the method in different settings.     

Some limitation on stein's phenomenon

We show that Stein's phenomenon is impossible for the following decision setting: the parameter space is compact, the loss function is the sum of coordinatewise strictly convex continuous loss functions, and the probability density function having the same support for every parameter θ is continuous in θ. Therefore, any coordinatewise admissible decision rule is admissible.     

Biodiversity of ant species along a disturbance gradient in residential environments of Puerto Rico

One of the most effective ways to describe the successional gradient of an environment is by using measures of biodiversity. We investigated the biodiversity of ant communities (known tramp/structure invaders) in an environment undergoing urban succession to characterize how ant communities changed along a disturbance gradient. Ant community dynamics were examined within three Puerto Rican housing developments of different ages. Within each development, we assessed the ant community using biodiversity measures of richness, abundance, diversity and evenness. We also studied changes in biodiversity within each development over time as well as how biodiversity related to food preferences within the ant communities. In general, the biodiversity measures increased as the age of the housing development increased. Monthly changes in biodiversity indicated that month was a better predictor of biodiversity in the most recently disturbed development, while the biodiversity in the older developments was less predictable from month to month. The biodiversity measures also suggested that the ant community in the youngest development was comprised mostly of generalist feeders. However, the older sites’ ant species appeared to have more specific feeding preferences. Based on the biodiversity measures of these ant communities, our findings suggest that the housing developments of different ages represented advancing stages of secondary succession. Furthermore, this study indicated that the succession of ant species occurs rapidly (<10 years) in urban environments, resulting in a relatively diverse ant community.