Friendships in late life: A rural-urban comparison

This study examines the friendship patterns of older adults living in rural and urban areas. The sample consisted of 132 urban adults and 126 rural adults, 65 years of age and older. Respondents were randomly selected and interviewed in their own homes. While both groups were involved in joint social activities and helping behaviors with their friends, there was a distinction in the type of involvement according to geographical location.Karen Roberto is Assistant Professor and Coordinator of the Gerontology Program at the University of Northern Colorado. Her current research interests include women's health issues in aging and older people's involvement with informal support networks. Dr. Roberto holds a Ph.D. in Human Development from Texas Tech University.Jean Pearson Scott is Associate Professor in the Department of Human Development and Family Studies at Texas Tech University. Dr. Scott earned her Ph.D. from the University of North Carolina at Greensboro and is currently conducting research on Alzheimers Disease in the family and the rural elderly.This is a revised version of a paper presented at the Families and Close Relationships: Individuals in Social Interaction Conference, Lubbock, TX, February, 1982.This study was supported by a grant from AARP Andrus Foundation and the Institute for University Research, College of Home Economics, Texas Tech University, Lubbock, Texas 79409.     

A Semi-parametric Bayesian Analysis of Survival Data Based on Lévy-driven Processes

In the presence of covariate information, the proportional hazards model is one of the most popular models. In this paper, in a Bayesian nonparametric framework, we use a Markov (Lévy-driven) process to model the baseline hazard rate. Previous Bayesian nonparametric models have been based on neutral to the right processes, which have a number of drawbacks, such as discreteness of the cumulative hazard function. We allow the covariates to be time dependent functions and develop a full posterior analysis via substitution sampling. A detailed illustration is presented.     

BULIMIA: THE TRANSGENERATIONAL VIEW*

Within families presenting with bulimia, there exist interactional patterns that can be said to enable, and perpetuate, the binge-eating and purging symptoms of the identified patient. A transgenerational treatment method is proposed, which not only intervenes in ongoing dysfunctional patterns, but also provides a frame for creating a therapeutic metaphor (“legacy”) to direct the therapy. Rationale and stages of the treatment process are outlined, and a case example is given to illustrate use of the transgenerational frame.     

Identifying Preferences for Conditional Cooperation Using Individual Beliefs

The relationship between contributions and elicited beliefs in a repeated two-person public good experiment is modeled with the help of a parsimounious random-utility function that allows for conditionally cooperative, opportunistic, and altruistic patterns of behavior. Under standard assumptions, a latent-class mixed logit specification with three sub-populations is shown to capture well heterogeneity in individual contribution levels over time, while also accomodating for different degrees of heteroscedasticity. The estimation results are consistent with the conjecture that the majority of players in public goods games are strongly conditional cooperators, with smaller fractions of the population leaning to opportunistic or altruistic behavior.     

Partial and inverse autocorrelations in portmanteau-type tests for time series

We present a decomposition of the correlation coefficient between x_t and x_t?k into three terms that include the partial and inverse autocorrelations. The first term accounts for the portion of the autocorrelation that is explained by the inner variables {x_t?1 , x_t?2 , …, x _{t? k+1}}, the second one measures the portion explained by the outer variables {x _t+1, x _t+2, } ∪ {x _t?k?1, x _t?k?2,…} and the third term measures the correlation between x _t and x_t?k given all other variables. These terms, squared and summed, can form the basis of three portmanteau-type tests that are able to detect both deviation from white noise and lack of fit of an entertained model. Quantiles of their asymptotic sample distributions are complicated to derive at an adequate level of accuracy, so they are approximated using the Monte Carlo method. A simulation experiment is carried out to investigate significance levels and power of each test, and compare them to the portmanteau test.     

A new mixture model on the simplex

This paper is meant to introduce a significant extension of the flexible Dirichlet (FD) distribution, which is a quite tractable special mixture model for compositional data, i.e. data representing vectors of proportions of a whole. The FD model displays several theoretical properties which make it suitable for inference, and fairly easy to handle from a computational viewpoint. However, the rigid type of mixture structure implied by the FD makes it unsuitable to describe many compositional datasets. Furthermore, the FD only allows for negative correlations. The new extended model, by considerably relaxing the strict constraints among clusters entailed by the FD, allows for a more general dependence structure (including positive correlations) and greatly expands its applicative potential. At the same time, it retains, to a large extent, its good properties. EM-type estimation procedures can be developed for this more complex model, including ad hoc reliable initialization methods, which permit to keep the computational issues at a rather uncomplicated level. Accurate evaluation of standard error estimates can be provided as well.     

Soil organic carbon stock in different urban land uses: high stock evidence in urban parks

Urban Ecosystems - Urban areas are major producers of atmospheric CO2 emissions, but at the same time they can offset some of the associated C losses by retaining stable organic carbon in their...     

Size does matter: Passive sampling in urban parks of a regional bat assemblage

Urban Ecosystems - We studied the occurrence of bats in urban parks in the city of Madrid (Spain), and the resulting patterns were compared with bat occurrence in the surrounding region. In this...     

Model-based clustering with determinant-and-shape constraint

Statistics and Computing - Model-based approaches to cluster analysis and mixture modeling often involve maximizing classification and mixture likelihoods. Without appropriate constrains on the...