Applications of quadrivariate exponential distribution to a three-unit warm standby system with dependent structure

Two-unit warm standby systems have been elaborately dealt within the literature. However, the study of standby systems with more than two units, though very relevant in state-of-the-art practical situations, has received little attention because of mathematical intricacies involved in analyzing them. Also, such systems have been studied assuming: (i) the lifetime or repair time of the units to be exponential, or (ii) the lifetime and repair time to be independent. The present contribution is an improvement in the state-of-the-art in the sense that three-unit warm standby system with dependent structure is shown to be capable of comprehensive analysis.     

Developing a clinical trial governance framework for pharmaceutical industry-funded clinical trials

ABSTRACT

Rising concerns relating to pharmaceutical sponsor bias in the conduct of clinical trials have compelled the need to develop a clinical trial governance framework. This article describes the development of the Conflict of Interest in Research (COIR), a clinical trial governance framework. The COIR, consisting of three process phases (initiation, concurrent, and ongoing), developed following a needs assessment, using a four-stage methodology, and evaluated against the International Conference on Harmonization--Good Clinical Practice (ICH-GCP) guidelines. The Conflict of Interest Resolution algorithm, the backbone of COIR, enables constant surveillance to detect/resolve conflicts at all stages of the clinical trial life-cycle. COIR promotes interaction between the regulatory system and the sponsors, independent of individuals. COIR enables rapid detection of scientific and financial conflicts, to prevent subject harm and, to assure optimal funds utilization, the latter feature helped to reduce a significant burden for the ethics committee, as it lacks financial expertise. COIR is a semi-automated Oracle system, requires manpower, and is affected by human expertise and subjectivity. Complete automation to overcome this limitation will still need human expertise to scale changing trial regulations. Nevertheless, the COIR has won the distinction of the “most favored site” from pharmaceutical sponsors and is anticipated to be adopted by other clinical trial sites.     

A Modification of a Percentile Estimation Procedure Based on Generalized Polya Urns

Adaptive designs find an important application in the estimation of unknown percentiles for an underlying dose-response curve. A nonparametric adaptive design was suggested by Mugno et al. (2004 Mugno, R.A., Zhus, W., Rosenberger, W.F. (2004). Adaptive urn designs for estimating several percentiles of a dose-response curve. Statist. Med. 23(13):2137–2150.[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]) to simultaneously estimate multiple percentiles of an unknown dose-response curve via generalized Polya urns. In this article, we examine the properties of the design proposed by Mugno et al. (2004 Mugno, R.A., Zhus, W., Rosenberger, W.F. (2004). Adaptive urn designs for estimating several percentiles of a dose-response curve. Statist. Med. 23(13):2137–2150.[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]) when delays in observing responses are encountered. Using simulations, we evaluate a modification of the design under varying group sizes. Our results demonstrate unbiased estimation with minimal loss in efficiency when compared to the original compound urn design.     

Maternal Health Care Seeking Behavior in a Post-Conflict HIPC: The Case of Rwanda

Rwanda is one of nine post-conflict heavily indebted poor countries (HIPC) of the world. There was a worsening of health indicators since the early nineties on account of conflict. In light of this, we examine factors affecting maternal health care seeking behavior in Rwanda using three rounds of Rwanda Demographic and Health Survey (RDHS) data (1992, 2000, and 2005). We find that progress towards increasing the share of assisted deliveries has been slow. There has been no significant increase in the proportion of women seeking antenatal care. This could partially explain why a large proportion of women continue to deliver at home without professional assistance. Further, women who gave birth in the 5 years preceding the 2000 RDHS are less likely to deliver in a health facility than those who gave birth in the 5 years preceding the 1992 RDHS. We do not find such a result for the year 2005. We also find that women are more likely to deliver at home with professional assistance in 2000 and 2005 compared to 1992.     

Effect of Conflict on Age at Marriage and Age at First Birth in Rwanda

Using Rwanda Demographic and Health Survey 2005 data, we estimate a Cox proportional hazard model to identify the determinants of age at marriage and age at first birth and whether these decisions were affected by conflict. We find that women living in clusters accounting for a larger proportion of sibling deaths in 1994, the year of the genocide, were more likely to marry later and have children later compared with those living in clusters accounting for a lower proportion of sibling deaths. Women living in regions with higher levels of under-five mortality were more likely to have their first child earlier compared with women living in regions with lower infant mortality. The age at marriage was probably affected by two reasons: the change in age structure and sex ratio of the population following the genocide, and the breakdown of kinship in the case of women who lost their siblings.     

Likelihood‐based inferences about the mean area under a longitudinal curve in the presence of observations subject to limits of detection

Comparison of groups in longitudinal studies is often conducted using the area under the outcome versus time curve. However, outcomes may be subject to censoring due to a limit of detection and specific methods that take informative missingness into account need to be applied. In this article, we present a unified model‐based method that accounts for both the within‐subject variability in the estimation of the area under the curve as well as the missingness mechanism in the event of censoring. Simulation results demonstrate that our proposed method has a significant advantage over traditionally implemented methods with regards to its inferential properties. A working example from an AIDS study is presented to demonstrate the applicability of our approach. Copyright © 2015 John Wiley & Sons, Ltd.