EFFECTS OF EXPOSURE ON PREVALENCE AND CUMULATIVE RELATIVE RISK: DIRECT AND INDIRECT EFFECTS IN A RECURSIVE HAZARD MODEL

This paper outlines decomposition methods for assessing how exposure affects prevalence and cumulative relative risk. Let     x     denote a vector of exogenous covariates and suppose that a single dimension of time   t   governs two event processes     T ₁  and   T ₂.    If the occurrence of the event     T ₁    determines entry into the risk of the event     T ₂,    then subgroup variation in     T ₁    will affect the prevalence     T ₂,    even if subgroups in the population are otherwise identical. Although researchers often acknowledge this phenomenon, the literature has not provided procedures to assess the magnitude of an exposure effect of     T ₁    on the prevalence of     T ₂.    We derive decompositions that assess how variation in exposure generated by direct and indirect effects of the covariates     x     affect measures of absolute and relative prevalence of     T ₂.    We employ a parametric but highly flexible specification for baseline hazard for the     T ₁  and   T ₂    processes and use the resulting parametric proportional hazard model to illustrate the direct and indirect effects of family structure when     T ₁    is age at first sexual intercourse and     T ₂    is age at a premarital first birth for data on a cohort of non-hispanic white U.S. women.     

Evaluation of two school‐based HIV prevention interventions in the border city of Tijuana,Mexico

This research project examined the individual and combined effectiveness of an HIV prevention workshop and a free condom distribution program in four high schools in Tijuana, Mexico. Adolescents (N = 320) completed baseline measures on sexual practices and theoretical correlates and participated in a two‐part study. In Study I, students were randomly assigned to an HIV prevention workshop or a control condition, with a 3‐month follow‐up assessment. Results indicate three significant workshop benefits regarding HIV transmission by altering sexual initiation, access to condoms, and traditional beliefs regarding condoms. In Study 2, we set up a condom distribution program at two of the participating schools, and students completed a 6‐month follow‐up assessment. Results indicate that exposure to the workshop followed by access to the condom distribution program yielded two beneficial results for reducing HIV transmission: moderating sexual initiation and increasing condom acquisition. Access to the condom distribution program alone had no effects on behavioral and psy‐chosocial correlates of HFV transmission. We discuss implications of these results.     

Xinhai remembered: from Han racial revolution to great revival of the Chinese nation

This article turns three different analytical mirrors onto the Xinhai Revolution – 1911, 1961, 2011 – in order to interrogate its evolving significance in the minds of China's Han ethnic and ruling elite. In particular, it seeks to demonstrates the discursive appropriation of the Qing nomadic frontier in the ways in which the 1911 Revolution is remembered and commemorated, exploring both the temporal and spatial dimensions of this appropriation, and how the revolution shifted from a bloody Han racial insurrection against Manchu power and privilege to a heroic celebration of the revival of a multiethnic Chinese nation-state in the face of foreign imperialism and oppression.     

Projektmanagement mit virtuellen Teams?

Globalisation and internationalisation of organisations as well as fast-paced development of modern electronic communication technologies require and support the implementation of globally distributed project teams. Members are working together in different locations and in different time zones. These facts have an impact on project work. This article tries to critically reflect the work of virtual project teams and it tries to answer the question, if we can speak about teamwork under such circumstances.     

Sex,Arts and Verbal Abilities: Three Further Indicators of How American Life is not Improving

Despite clear evidence that Americans’ economic standard of living has improved over the last half-century in terms of income, ownership of technology and housing among other indicators, there is scant evidence from non-economic quality-of-life (QOL) indicators of improved life quality to parallel these economic gains. The present article adds to this list in showing little if any progress in three QOL indicators (the first two about time and activity) that have received less or no attention in the social indicators literature, namely (1) frequency of the highly enjoyable activity of sex, (2) participation in various serious arts activities and (3) scores of verbal ability. The data on sexual activity and verbal ability come from the 1974–2008 General Social Surveys (GSS) from the University of Chicago, and for the arts from the 2008 Survey of Public Participation in the Arts (SPPA) conducted by the US Census Bureau for the National Endowment for the Arts since 1982. All three surveys interviewed nationally representative samples, with over 70% response rates and sample sizes of more than 15,000 adults. The GSS data on sexual frequency show no significant increase in estimated frequency of sex since 1989, despite its strong appeal and the availability of new societal conveniences. This held both before and after adjustment for the age, marital status and education in the population; contrary to expectation, working long hours was associated with increased sex both before and after adjustment for these other demographic predictors. The SPPA trend data on arts participation actually showed a decline in participation, especially after adjustment for its major predictor of years of education; again no decreased participation was found among those working long hours. While scores on verbal ability in the GSS have stayed rather steady since 1974, they have decreased after MCA adjustment for the increased college education in more recent years, as documented by Nie et al. (2009). Thus, contrary to expectations, increases in public education have not been accompanied by improvements on these three indicators.     

The eigenstructure of block-structured correlation matrices and its implications for principal component analysis

Block-structured correlation matrices are correlation matrices in which the p variables are subdivided into homogeneous groups, with equal correlations for variables within each group, and equal correlations between any given pair of variables from different groups. Block-structured correlation matrices arise as approximations for certain data sets’ true correlation matrices. A block structure in a correlation matrix entails a certain number of properties regarding its eigendecomposition and, therefore, a principal component analysis of the underlying data. This paper explores these properties, both from an algebraic and a geometric perspective, and discusses their robustness. Suggestions are also made regarding the choice of variables to be subjected to a principal component analysis, when in the presence of (approximately) block-structured variables.     

Exact moments of a ratio of two positive quadratic forms in normal variables

This paper derives an expression for rth raw moment of aratio of two quadratic forms in normal variables in terms of' a

convergent infinite series. Computational aspects of this formula are explored by considering a particular case.     

A perspective of composite sampling

Composite samples are formed by physically mixing samples. Usually, composite samples are used to reduce the overall cost associated with analytical procedures that must be performed on each sample, but they can also be used to protect the privacy of individuals.

Composite sampling can reduce the cost of identifying individual cases that have a certain trait, such as those with a rare disease or those exceeding pollution-level standards. Not much is lost by applying this method as long as the trait is relatively rare.

Composite sampling can reduce the cost of estimating the mean of some process. When samples are composited, the ability to estimate the variance is lost. In spite of this, the potential savings are so great that composite samples have been used.

Much of this paper deasl with the variance of estimators based on composite sampling when the porportions of hte original samples comprising the composite sample are actually random. Taking repeated samples and measurements on several composite samples complicates the prodcedure, but allows the estimation of between and within variation as well as measurement error.