Modelling human immunodeficiency virus ribonucleic acid levels with finite mixtures for censored longitudinal data

The measurement of human immunodeficiency virus ribonucleic acid levels over time leads to censored longitudinal data. Suitable models for dynamic modelling of these levels need to take this data characteristic into account. If groups of patients with different developments of the levels over time are suspected the model class of finite mixtures of mixed effects models with censored data is required. We describe the model specification and derive the estimation with a suitable expectation-maximization algorithm. We propose a convenient implementation using closed form formulae for the expected mean and variance of the truncated multivariate distribution. Only efficient evaluation of the cumulative multivariate normal distribution function is required. Model selection as well as methods for inference are discussed. The application is demonstrated on the clinical trial ACTG 315 data.     

Reports of Conferences,Institutes, and Seminars

In the span of four weeks, from late March to early April 2008, three important technical services conferences were held: the Electronic Resources & Libraries Conference, the New England Technical Services Librarians Conference, and the North Carolina Serials Conference.     

Prosocial Behavior: Long‐term Trajectories and Psychosocial Outcomes

This study investigated developmental trajectories for prosocial behavior for a sample followed from the age of 10–18 and examined possible adjustment outcomes associated with membership in different trajectory groups. Participants were 136 boys and 148 girls, their teachers, and their parents (19.4 percent African‐American, 2.4 percent Asian, 51.9 percent Caucasian, 19.5 percent Hispanic, and 5.8 percent other). Teachers rated children's prosocial behavior yearly in grades 4–12. At the end of the 12th grade year, teachers, parents, and participants reported externalizing behaviors and participants reported internalizing symptoms, narcissism, and features of borderline personality disorder. Results suggested that prosocial behavior remained stable from middle childhood through late adolescence. Group‐based mixture modeling revealed three prosocial trajectory groups: low (18.7 percent), medium (52.8 percent), and high (29.6 percent). Membership in the high prosocial trajectory group predicted lower levels of externalizing behavior as compared with the low prosocial trajectory group, and for girls, lower levels of internalizing symptoms. Membership in the medium prosocial trajectory group also predicted being lower on externalizing behaviors. Membership in the high prosocial trajectory group predicted lower levels of borderline personality features for girls only.     

Impact of physical activity and sedentary behaviour on fall risks in older people: a systematic review and meta-analysis of observational studies

The objective of this work was to summarise and evaluate the evidence showing that physical activity is a protector factor as regards falls in older people. Relevant studies were identified through a systematic search in the MEDLINE and Cochrane Library, under the keywords of accidental fall/numerical data and risk factors, and with the bibliographies of retrieved papers. The combined odds ratio (OR) [95% confidence interval] for physical activity was 0.75 [0.64, 0.88] with moderate heterogeneity (I ²?=?33%). For fall injury, it was 0.59 [0.47, 0.74] and, for falls in general, it rose to 0.94 [0.76, 1.17] with nil heterogeneity. The combined OR for sedentary factors was 1.14 [1.10, 1.82] with moderate heterogeneity (I ²?=?36%). Regular physical activity in daily life yields significant reduction in falls in older people, especially falls with injuries.     

Vision and state health department public relations practitioners: Prepared to lead?

Visions are important to organizational effectiveness. Although providing vision has been identified as one of the behaviors that best captures organization-wide public relations leadership, little public relations research has focused on vision. Similarly, state health departments have drawn little interest among public relations scholars even though states are a central part of the nation's public health system. This study addressed the perceptions of the top public relations professionals at state health departments concerning vision and their involvement in the visioning process. The practitioners were nearly unanimous in their belief that organizational visions are important. However, results indicate that some top public relations practitioners at state health departments are not prepared to make optimal contributions to the visioning process. In order to take full advantage of opportunities to serve as organization-wide leaders, public relations practitioners should seek out information about visioning in order help chart their organization's future and enhance their careers.     

Lies and slander: truth-telling in repeated matching games with private monitoring

Incentives for cooperation may be enhanced substantially if a player can rely on the entire community to punish a partner who failed to cooperate. The ability of a player to report a defection to others can constitute a strong deterrent against defection if this report triggers a punishment imposed by the whole community. This paper studies the truth-telling problem in such a context. The paper presents a sequential equilibrium that supports cooperation in which a player unilaterally reports the play of a partner with strict incentives for truth-telling. It is shown, however, that desirable properties of equilibria described in the previous literature that assume truth-telling no longer exist. The implications of the results for practical examples, such as trading on eBay, are discussed.     

Time series count data regression

The count data model studied in the paper extends the Poisson model by al-lowing for overdispersion and serial correlation. Alternative approaches to esti-mate nuisance parameters, required for the correction of the Poisson maximum likelihood covariance matrix estimator and for a quasi-likelihood estimator, are studied. The estimators are evaluated by finite sample Monte Carlo experi-mentation. It is found that the Poisson maximum likelihood estimator with corrected covariance matrix estimators provide reliable inferences for longer time series. Overdispersion test statistics are wellbehaved, while conventional portmanteau statistics for white noise have too large sizes. Two empirical illustrations are included.