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In this paper, we propose a novel frailty model for modeling unobserved heterogeneity present in survival data. Our model is derived by using a weighted Lindley distribution as the frailty distribution. The respective frailty distribution has a simple Laplace transform function which is useful to obtain marginal survival and hazard functions. We assume hazard functions of the Weibull and Gompertz distributions as the baseline hazard functions. A classical inference procedure based on the maximum likelihood method is presented. Extensive simulation studies are further performed to verify the behavior of maximum likelihood estimators under different proportions of right-censoring and to assess the performance of the likelihood ratio test to detect unobserved heterogeneity in different sample sizes. Finally, to demonstrate the applicability of the proposed model, we use it to analyze a medical dataset from a population-based study of incident cases of lung cancer diagnosed in the state of São Paulo, Brazil.

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The Birnbaum-Saunders distribution is a widely studied model with diverse applications. Its origins are in the modeling of lifetimes associated with material fatigue. By using a motivating example, we show that, even when lifetime data related to fatigue are modeled, the Birnbaum-Saunders distribution can be unsuitable to fit these data in the distribution tails. Based on the nice properties of the Birnbaum-Saunders model, in this work, we use a modified skew-normal distribution to construct such a model. This allows us to obtain flexibility in skewness and kurtosis, which is controlled by a shape parameter. We provide a mathematical characterization of this new type of Birnbaum-Saunders distribution and then its statistical characterization is derived by using the maximum-likelihood method, including the associated information matrices. In order to improve the inferential performance, we correct the bias of the corresponding estimators, which is supported by a simulation study. To conclude our investigation, we retake the motivating example based on fatigue life data to show the good agreement between the new type of Birnbaum-Saunders distribution proposed in this work and the data, reporting its potential applications.

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Abstract An unsteady plan for curriculum development and supportive issues in physical education (PE) has created confusion among professionals. The purpose of this research is to investigate the factors perceived as important in the development of quality physical education (QPE) by professionals in Latin American (LA) countries. A questionnaire consisting of 24 items based on QPE was responded by 468 professionals collected from 6 LA cities. An exploratory factor analysis (EFA) of the 24 items using ML extraction and direct oblimin rotation were applied, and the retained 17 items were clustered in a three factor solution referred to as, Development and Supportive Elements for QPE in School (DSFQPE) (α = .935), Core Value of QPEtabl (CVPE) (α = .890), and Curriculum Arrangement of Physical Activities (CAPA) (α = .850). The retained items indicated excellent properties and the basic framework as perceived by professionals from PE in LA countries as important in the investigation of QPE.

Resumo Um plano instável para o desenvolvimento de currículos e questões de apoio na educação física (PE) criou confusão entre os profissionais. O objetivo desta pesquisa é investigar os fatores percebidos como importantes no desenvolvimento da educação física de qualidade (QPE) por profissionais de países da América Latina (AL). Um questionário composto por 24 itens com base no QPE foi respondido por 468 profissionais coletados em 6 cidades da América Latina. Uma análise fatorial exploratória dos 24 itens usando extração ML e rotação obliminar direta foram aplicados, e os 17 itens retidos foram agrupados em uma solução de três fatores denominada Elementos de Desenvolvimento e Suporte para QPE na Escola (DSFQPE) (α = 0,935), Valor essencial do QPE (CVPE) (α = 0,890) e Arranjo Curricular das Atividades Físicas (CAPA) (α = 0,850). Os itens retidos indicaram propriedades excelentes e o referencial básico percebido pelos profissionais de EF em países da América Latina como importante na investigação do PEQ.

Resumen Un plan inestable para el desarrollo curricular y aspectos de apoyo para la educación física (EF) han creado confusión entre los profesionales. El propósito de esta investigación es investigar los factores percibidos como importantes en el desarrollo de la educación física de calidad (EFC) por profesionales en países de América Latina (AL). Un cuestionario que consta de 24 ítems basados en EFC fue respondido por 468 profesionales recolectados en 6 ciudades de LA. Se aplicó un Análisis factorial exploratorio de los 24 ítems que utilizan extracción ML y rotación oblicua directa, y los 17 ítems retenidos se agruparon en una solución de tres factores denominada Elementos de desarrollo y de apoyo para EFC en la escuela (EDAEFC) (α = 0,935); Valor principal de EFC (CVPE) (α = 0,890) y Arreglo del plan de actividades físicas (CAPA) (α = 0,850). Los ítems retenidos indicaron excelentes propiedades y el marco básico es percibido por los profesionales de EF en los países de AL como importante en la investigación de EFC.

RESUMO

In survival models, some covariates affecting the lifetime could not be observed or measured. These covariates may correspond to environmental or genetic factors and be considered as a random effect related to a frailty of the individuals explaining their survival times. We propose a methodology based on a Birnbaum-Saunders frailty regression model, which can be applied to censored or uncensored data. Maximum-likelihood methods are used to estimate the model parameters and to derive local influence techniques. Diagnostic tools are important in regression to detect anomalies, as departures from error assumptions and presence of outliers and influential cases. Normal curvatures for local influence under different perturbations are computed and two types of residuals are introduced. Two examples with uncensored and censored real-world data illustrate the proposed methodology. Comparison with classical frailty models is carried out in these examples, which shows the superiority of the proposed model.

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Neurons transmit information as action potentials or spikes. Due to the inherent randomness of the inter-spike intervals (ISIs), probabilistic models are often used for their description. Cumulative damage (CD) distributions are a family of probabilistic models that has been widely considered for describing time-related cumulative processes. This family allows us to consider certain deterministic principles for modeling ISIs from a probabilistic viewpoint and to link its parameters to values with biological interpretation. The CD family includes the Birnbaum-Saunders and inverse Gaussian distributions, which possess distinctive properties and theoretical arguments useful for ISI description. We expand the use of CD distributions to the modeling of neural spiking behavior, mainly by testing the suitability of the Birnbaum-Saunders distribution, which has not been studied in the setting of neural activity. We validate this expansion with original experimental and simulated electrophysiological data.

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Accurate estimates of the penetrance rate of autosomal dominant conditions are important, among other issues, for optimizing recurrence risks in genetic counseling. The present work on penetrance rate estimation from pedigree data considers the following situations: 1) estimation of the penetrance rate K (brief review of the method); 2) construction of exact credible intervals for K estimates; 3) specificity and heterogeneity issues; 4) penetrance rate estimates obtained through molecular testing of families; 5) lack of information about the phenotype of the pedigree generator; 6) genealogies containing grouped parent-offspring information; 7) ascertainment issues responsible for the inflation of K estimates.

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Neste trabalho, objetivou-se comparar três estimadores do coeficiente de endogamia, F, em uma população diplóide com dois alelos, utilizando-se dados de frequências alélicas em amostras de indíviduos, com diferentes tamanhos obtidas em populações simuladas, por meio do software SAS. Foi avaliado o estimador de F, obtido pela análise de variância de frequências alélicas, o estimador considerando o método dos momentos e o estimador pelo método da máxima verossimilhança. Os resultados encontrados para a média e variância os estimadores, a partir de 1000 estimativas de F, calculadas para cada tamanho de amostra, mostraram que os três estimadores são tendenciosos. Entretanto, de maneira geral, observou-se que o estimador considerando a análise de variância foi menos tendencioso e apresentou menor variância, quando o coeficiente de endogamia da população foi alto. Para tamanho de amostra superior a 50, os três estimadores tiveram comportamento semelhante, independente da frequência alélica e da endogamia da população.

The present work evaluated the properties of three estimators of the inbreeding coefficient, F, in a diploid population with two alleles, using data of gene frequencies in individuals from random samples obtained from populations simulated through the SAS. We evaluated the estimators of F obtained by variance analysis of allelic frequencies, obtained by moment method, and estimator obtained by maximum likelihood method. The analysis of the means and variances of the estimators, obtained from 1000 estimates of F, calculated for each sample size, demonstrated that the three estimators were biased. However, it was observed that the estimator obtained from univariate analysis was less biased and presented smaller variance, when the inbreeding coefficient in the population was elevated, while for populations with low inbreeding, the variance of the estimator obtained by the multivariate analysis was smaller.