THE CALCULATION OF CONFIDENCE REGIONS FOR EIGENVECTORS

An explicit algorithm is given for constructing a confidence region on the appropriate unit sphere for an eigenvector, given a large sample. It is assumed the eigenvector corresponds to the largest eigenvalue of Exx^T, a matrix with distinct eigenvalues, and that the estimation uses n^-1S?x_ix_ix^T. While the theory is generally applicable, the writer has in mind the special case where ∥x∥= 1 i.e. directional data.     

Stochastic volatility modelling in continuous time with general marginal distributions: Inference,prediction and model selection

We compare results for stochastic volatility models where the underlying volatility process having generalized inverse Gaussian (GIG) and tempered stable marginal laws. We use a continuous time stochastic volatility model where the volatility follows an Ornstein–Uhlenbeck stochastic differential equation driven by a Lévy process. A model for long-range dependence is also considered, its merit and practical relevance discussed. We find that the full GIG and a special case, the inverse gamma, marginal distributions accurately fit real data. Inference is carried out in a Bayesian framework, with computation using Markov chain Monte Carlo (MCMC). We develop an MCMC algorithm that can be used for a general marginal model.     

Modelling three-dimensional trajectories by using Bézier curves with application to hand motion

Summary.  A modelling approach for three-dimensional trajectories with particular application to hand reaching motions is described. Bézier curves are defined by control points which have a convenient geometrical interpretation. A fitting method for the control points to trajectory data is described. These fitted control points are then linked to covariates of interest by using a regression model. This allows the prediction of new trajectories and the ability to model the variability in trajectories. The methodology is illustrated with an application to hand trajectory modelling for ergonomics. Motion capture was used to collect a total of about 2000 hand trajectories performed by 20 subjects to a variety of targets. A simple model with strong predictive performance and interpretablility is developed. The use of hand trajectory models in the digital human models for virtual manufacturing applications is discussed.     

Spatio-temporal improvised explosive device monitoring: improving detection to minimise attacks

The improvised explosive device (IED) is a weapon of strategic influence on today's battlefield. IED detonations occur predominantly on roads, footpaths, or trails. Therefore, locations are best described when constrained to the road network, and some spaces on the network are more dangerous at specific times of the day. We propose a statistical model that reduces the spatial location to one dimension and uses a cyclic time as a second dimension. Based on the Poisson process methodology, we develop normalised, inhomogeneous, bivariate intensity functions measuring the threat of attack to support resourcing decisions. A simulation and an analysis of attacks on a main supply route in Baghdad are given to illustrate the proposed methods. Additionally, we provide an overview of the growing demand for the analysis efforts in support of operations in Afghanistan and Iraq, and provide an extensive literature review of developments in counter-IED analysis.     

Building Citizenship: How Student Voice in Service-Learning Develops Civic Values

Objective . Though many decry the decline in political participation and interest, few academic studies present a clear approach to help reverse these trends. This paper examines the impact of service-learning programs on students' self-concept, political engagement, and attitudes toward out-groups. Methods . The data come from a pre and post survey given to more than 200 high school students in 10 different schools. We use Huber regression to assess the impact of student voice in the service-learning project on six dependent variables. Results . We show that if students are involved in service-learning projects in which they have a high degree of voice and ownership, their self-concept and political engagement will improve, and they become more tolerant toward out-groups. Conclusion . In short, having a voice in service-learning programs builds citizenship.     

An Integrated Physical Dispersion and Behavioral Response Model for Risk Assessment of Radiological Dispersion Device (RDD) Events

A radiological dispersion device (RDD) or "dirty" bomb is a conventional explosive wrapped in radiological material. Terrorists may use an RDD to disperse radioactive material across a populated area, causing casualties and/or economic damage. Nearly all risk assessment models for RDDs make unrealistic assumptions about public behavior in their health assessments, including assumptions that the public would stand outside in a single location indefinitely. In this article, we describe an approach for assessing the risks of RDD events incorporating both physical dispersion and behavioral response variables. The general approach is tested using the City of Pittsburgh, Pennsylvania as a case study. Atmospheric models simulate an RDD attack and its likely fallout, while radiation exposure models assess fatal cancer risk. We model different geographical distributions of the population based on time of day. We evaluate aggregate health impacts for different public responses (i.e., sheltering-in-place, evacuating). We find that current RDD models in use can be improved with the integration of behavioral components. Using the results from the model, we show how risk varies across several behavioral and physical variables. We show that the best policy to recommend to the public depends on many different variables, such as the amount of trauma at ground zero, the capability of emergency responders to get trauma victims to local hospitals quickly and efficiently, how quickly evacuations can take place in the city, and the amount of shielding available for shelterers. Using a parametric analysis, we develop behaviorally realistic risk assessments, we identify variables that can affect an optimal risk reduction policy, and we find that decision making can be improved by evaluating the tradeoff between trauma and cancer fatalities for various RDD scenarios before they occur.     

LOWER BOUNDS FOR THE DIVERGENCE OF DIRECTIONAL AND AXIAL ESTIMATORS

Consider estimation of a unit vector parameter a in two classes of distributions. In the first, α is a direction. In the second, α is an axis, so that –α and α are equivalent: the aim is to obtain the projector αα^t. In each case the paper uses first principles to define measures of the divergence of such estimators and derives lower bounds for them. These bounds are computed explicitly for the Fisher-Von Mises and Scheidegger-Watson densities on the g-dimensional sphere, ω_q. In the latter case, the tightness of the bound is established by simulations.     

ON QUANTILES OF SUMS

In this paper we investigate the relationship between the quantiles of a sum of independent continuous random variables and those of its components. Results concerning this relationship are given for the special cases of symmetric distributions, gamma distributions, and for the difference of identically distributed random variables.     

Gender and homophily: Differences in male and female association in Blau space

Homophily, the tendency for similar individuals to associate, is one of the most robust findings in social science. Despite this robustness, we have less information about how personal characteristics relate to differences in the strength of homophily. Nor do we know much about the impact of personal characteristics on judgments of relative dissimilarity. The present study compares the strength of age, religious, and educational homophily for male and female non-kin ties using network data from the 1985 General Social Survey. It also compares the patterning of ties among dissimilar alters for both sexes. The results of this exploratory effort indicate that males and females are almost equally homophilous, although religious homophily exerts a stronger influence on females than males. Males and females do, however, differ in their tendency to associate with certain types of dissimilar alters. Education is essentially uniform for both sexes, religious difference is more important for females than males, and those over sixty or under thirty are less different from the middle categories of age for females than for males. The results suggest that males are able to bridge larger areas of social space in their non-kin interpersonal networks and likely accumulate greater social capital as a consequence.