Estimating the structural dimension of regressions via parametric inverse regression

A new estimation method for the dimension of a regression at the outset of an analysis is proposed. A linear subspace spanned by projections of the regressor vector X , which contains part or all of the modelling information for the regression of a vector Y on X , and its dimension are estimated via the means of parametric inverse regression. Smooth parametric curves are fitted to the p inverse regressions via a multivariate linear model. No restrictions are placed on the distribution of the regressors. The estimate of the dimension of the regression is based on optimal estimation procedures. A simulation study shows the method to be more powerful than sliced inverse regression in some situations.     

The Transformative Power of Youth Grants: Sparks and Ripples of Change Affecting Marginalised Youth and their Communities

This study, based on research into a youth empowerment initiative in Canada, examines the transformational power of youth grants for marginalised youth and their communities. The positive changes on individual youth included increased confidence and skills, as well as strengthened social interactions between youth, and involved adults and organisations. To leverage grant impact, we identify the critical role of creating accountability at multiple levels, promoting sharing among grantees, and fostering allies and system thinkers. The evaluation points to the potential of grants for changing community's perception that youth are incapable of fostering community youth development.     

Robust inference for bivariate point processes

In the analysis of recurrent events where the primary interest lies in studying covariate effects on the expected number of events occurring over a period of time, it is appealing to base models on the cumulative mean function (CMF) of the processes (Lawless & Nadeau 1995). In many chronic diseases, however, more than one type of event is manifested. Here we develop a robust inference procedure for joint regression models for the CMFs arising from a bivariate point process. Consistent parameter estimates with robust variance estimates are obtained via unbiased estimating functions for the CMFs. In most situations, the covariance structure of the bivariate point processes is difficult to specify correctly, but when it is known, an optimal estimating function for the CMFs can be obtained. As a convenient model for more general settings, we suggest the use of the estimating functions arising from bivariate mixed Poisson processes. Simulation studies demonstrate that the estimators based on this working model are practically unbiased with robust variance estimates. Furthermore, hypothesis tests may be based on the generalized Wald or generalized score tests. Data from a trial of patients with bronchial asthma are analyzed to illustrate the estimation and inference procedures.     

Peers influence the tobacco and alcohol use of Chinese adolescents

This two-wave longitudinal study examined peer selection and influence pertaining to tobacco and alcohol use by adolescents and their friends in a sample of 854 Chinese adolescents (384 girls: mean age = 13.33 years). Participants nominated friends and self-reported their tobacco and alcohol use at seventh and again at eighth grade. Longitudinal social network analyses revealed evidence of friend influence but not selection over smoking and drinking. Boys increased their levels of smoking at rates greater than that of girls, but no sex moderation of either selection or influence was found. In interpreting these results, it is important to understand the gender norms for Chinese boys and girls and the cultural context of tobacco and alcohol use.     

Female-headed households in nonmetropolitan areas: Housing and demographic characteristics

This article describes selected demographic and housing characteristics of nonmetropolitan female-headed households. It compares nonmetropolitan female householders with the average U.S. household, including regional differences. Female heads are older and more likely to have members in poor health than U.S. households on average. Female heads are also more likely to be in poverty and to experience housing poverty. Although the female householders do not suffer from space and quality problems, housing affordability is a problem. Most female heads live in owned, single-family dwellings and are more likely to live in mobile homes than the average U.S. household. This research was funded under the auspices of the U.S. Department of Agriculture, Cooperative State Research Service, and the experiment stations in Idaho, Indiana (Purdue University), Iowa, Minnesota, Missouri, Nebraska, and New York (Cornell University). Also supporting the research were East Carolina University, Illinois State University, Kansas State University, and Western Michigan University. The authors thank Mary Ann Horvath and Roxanne Miller for their assistance in preparing the figures and document. She received her Ph.D. from Oklahoma State University. Her work includes research in housing and the economic well-being of women. She received her Ph.D. from The Ohio State University. Her research interests include housing and neighborhood assessment and women and public policy issues.     

Mixture and mixture–process variable experiments for pharmaceutical applications

Many experiments in research and development in the pharmaceutical industry involve mixture components. These are experiments in which the experimental factors are the ingredients of a mixture and the response variable is a function of the relative proportion of each ingredient, not its absolute amount. Thus the mixture ingredients cannot be varied independently. A common variation of the mixture experiment occurs when there are also one or more process factors that can be varied independently of each other and of the mixture components, leading to a mixture–process variable experiment. We discuss the design and analysis of these types of experiments, using tablet formulation as an example. Our objective is to encourage greater utilization of these techniques in pharmaceutical research and development. Copyright © 2004 John Wiley & Sons Ltd.