Block and Basu bivariate lifetime distribution in the presence of cure fraction

This paper presents estimates for the parameters included in the Block and Basu bivariate lifetime distributions in the presence of covariates and cure fraction, applied to analyze survival data when some individuals may never experience the event of interest and two lifetimes are associated with each unit. A Bayesian procedure is used to get point and confidence intervals for the unknown parameters. Posterior summaries of interest are obtained using standard Markov Chain Monte Carlo methods in rjags package for R software. An illustration of the proposed methodology is given for a Diabetic Retinopathy Study data set.     

A Bayesian model for estimating the malaria transition probabilities considering individuals lost to follow-up

It is known that patients may cease participating in a longitudinal study and become lost to follow-up. The objective of this article is to present a Bayesian model to estimate the malaria transition probabilities considering individuals lost to follow-up. We consider a homogeneous population, and it is assumed that the considered period of time is small enough to avoid two or more transitions from one state of health to another. The proposed model is based on a Gibbs sampling algorithm that uses information of lost to follow-up at the end of the longitudinal study. To simulate the unknown number of individuals with positive and negative states of malaria at the end of the study and lost to follow-up, two latent variables were introduced in the model. We used a real data set and a simulated data to illustrate the application of the methodology. The proposed model showed a good fit to these data sets, and the algorithm did not show problems of convergence or lack of identifiability. We conclude that the proposed model is a good alternative to estimate probabilities of transitions from one state of health to the other in studies with low adherence to follow-up.     

On the Measurement of Interpersonal Trust Transfer: Proposal of Indexes

This paper investigates the measurement of trust transfer in interpersonal contexts. Despite the importance of this topic, little evidence of comparable indicators exists to fill the current gap in knowledge regarding the measurement of interpersonal transference of trust and its reciprocal. We propose a modification of the classical structure of a widely accepted experimental setting for analyzing trust (i.e. a trust game) and build two indexes for the measurement of trust transfer and its reciprocation. Several properties of these indicators are investigated to examine their robustness and accuracy for measuring the transference of interpersonal trust. Furthermore, using data from our own modified trust game, we provide an empirical examination of both indexes. The results show that the existence of a mutually known third party fosters a stronger willingness to achieve cooperative behavior in an anonymous trust game; thus, the transference of interpersonal trust works in both directions of the dyad.     

Improved Approximation for Breakpoint Graph Decomposition and Sorting by Reversals

Sorting by Reversals (SBR) is one of the most widely studied models of genome rearrangements in computational molecular biology. At present, is the best known approximation ratio achievable in polynomial time for SBR. A very closely related problem, called Breakpoint Graph Decomposition (BGD), calls for a largest collection of edge disjoint cycles in a suitably-defined graph. It has been shown that for almost all instances SBR is equivalent to BGD, in the sense that any solution of the latter corresponds to a solution of the former having the same value. In this paper, we show how to improve the approximation ratio achievable in polynomial time for BGD, from the previously known to for any > 0. Combined with the results in (Caprara, Journal of Combinatorial Optimization, vol. 3, pp. 149–182, 1999b), this yields the same approximation guarantee for n! – O((n – 5)!) out of the n! instances of SBR on permutations with n elements. Our result uses the best known approximation algorithms for Stable Set on graphs with maximum degree 4 as well as for Set Packing where the maximum size of a set is 6. Any improvement in the ratio achieved by these approximation algorithms will yield an automatic improvement of our result.     

Psychophysical conditions of air traffic controllers evaluated by the standard shiftwork index

Abstract

In the ambit of a large epidemiological survey on the Italian population of air traffic controllers, an evaluation of their health conditions was carried out using the Standard Shiftwork Index (SSI). The study took into consideration 572 male air traffic controllers, aged between 23 and 59 years, of whom 301 were engaged in three large Regional Centres, 189 in thirteen Airport Towers and 82. formerly active controllers, were working in administrative offices. The former controllers showed worse health levels, in particular minor psychological disorders and chronic fatigue. Sixteen of them had been transferred to administrative jobs because of health impairment, owing to severe diseases of the nervous, gastrointestinal and cardiovascular systems. Such disorders, and musculoskeletal ones, were mostly reported by the active controllers. The controllers engaged in Regional Centres showed more sleep disturbances than those engaged in towers. Beside age, some personal characteristics appeared to influence health and well-being. Neuroticism was correlated with chronic fatigue, digestive and cardiovascular complaints, minor psychological disorders, cognitive and somatic anxiety. On the other hand, morningness was correlated negatively with sleep disturbances on morning shift, and positively with sleep duration both on morning shift and rest days.     

Structure and composition of woody plants in urban forest remnants with different adjacent land-use and slope aspect

The plant community in the karst forest is influenced by mesoclimatic conditions, such as temperature and humidity and these conditions are in turn influenced by topographic features. Urban areas adjacent to karstic forest remnants also have the potential to influence mesoclimatic variables and may serve as a source of exotic species. We described the temperature and relative humidity of karstic forest remnants at slopes with combinations of either southeast (SE) or northwest (NW) aspect, and adjacent to either urban (URB) or secondary forest (SF). We also compared forest structure and composition on these slopes to understand the interaction between forest aspect and adjacent land use on the plant community. URB-SE slopes had highest temperature and lowest humidity among all adjacent land use-aspect combinations. Understory species in SE slopes had similar richness and diversity independently of adjacent land use, however within NW aspect, slopes adjacent to urban areas showed higher values than slopes adjacent secondary forest. Canopy trees species in slopes adjacent to secondary forest were more diverse and rich in SE than in NW, although no differences between aspects were detected within URB-adjacent slopes. Understory species composition was different among the four land use-aspect combinations. However, composition of canopy trees species was different only between aspect types. Most exotic species in the sites were associated with previous agricultural practices and not with current land use. Our results show a temporal and spatial influence of anthropogenic systems on the plant community in karstic forest remnants at a suburban area of Puerto Rico.     

Population and Deforestation in Costa Rica

This paper addresses a central debate in research and policy on population and environment, namely the extent to which rapid population growth is associated with the massive deforestation currently underway in the tropics. We utilize the experience of Costa Rica during the last forty years to illustrate what the main issues are, discuss the history of deforestation in that country, and present results from conventional regression methods and from the application of spatial analyses. These analyses enable us to estimate the magnitude of the relation between population and deforestation and to identify the factors that are responsible for the linkage between them.     

Modeling healthcare costs in simultaneous presence of asymmetry,heteroscedasticity and correlation

Highly skewed outcome distributions observed across clusters are common in medical research. The aim of this paper is to understand how regression models widely used for accommodating asymmetry fit clustered data under heteroscedasticity. In a simulation study, we provide evidence on the performance of the Gamma Generalized Linear Mixed Model (GLMM) and log-Linear Mixed-Effect (LME) model under a variety of data-generating mechanisms. Two case studies from health expenditures literature, the cost of strategies after myocardial infarction randomized clinical trial on the cost of strategies after myocardial infarction and the European Pressure Ulcer Advisory Panel hospital prevalence survey of pressure ulcers, are analyzed and discussed. According to simulation results, the log-LME model for a Gamma response can lead to estimations that are biased by as much as 10% of the true value, depending on the error variance. In the Gamma GLMM, the bias never exceeds 1%, regardless of the extent of heteroscedasticity, and the confidence intervals perform as nominally stated under most conditions. The Gamma GLMM with a log link seems to be more robust to both Gamma and log-normal generating mechanisms than the log-LME model.