The log-exponentiated Weibull regression model for interval-censored data

In interval-censored survival data, the event of interest is not observed exactly but is only known to occur within some time interval. Such data appear very frequently. In this paper, we are concerned only with parametric forms, and so a location-scale regression model based on the exponentiated Weibull distribution is proposed for modeling interval-censored data. We show that the proposed log-exponentiated Weibull regression model for interval-censored data represents a parametric family of models that include other regression models that are broadly used in lifetime data analysis. Assuming the use of interval-censored data, we employ a frequentist analysis, a jackknife estimator, a parametric bootstrap and a Bayesian analysis for the parameters of the proposed model. We derive the appropriate matrices for assessing local influences on the parameter estimates under different perturbation schemes and present some ways to assess global influences. Furthermore, for different parameter settings, sample sizes and censoring percentages, various simulations are performed; in addition, the empirical distribution of some modified residuals are displayed and compared with the standard normal distribution. These studies suggest that the residual analysis usually performed in normal linear regression models can be straightforwardly extended to a modified deviance residual in log-exponentiated Weibull regression models for interval-censored data. (C) 2009 Elsevier B.V. All rights reserved.

Deviance residuals in generalised log-gamma regression models with censored observations

In this article, we compare three residuals based on the deviance component in generalised log-gamma regression models with censored observations. For different parameter settings, sample sizes and censoring percentages, various simulation studies are performed and the empirical distribution of each residual is displayed and compared with the standard normal distribution. For all cases studied, the empirical distributions of the proposed residuals are in general symmetric around zero, but only a martingale-type residual presented negligible kurtosis for the majority of the cases studied. These studies suggest that the residual analysis usually performed in normal linear regression models can be straightforwardly extended for the martingale-type residual in generalised log-gamma regression models with censored data. A lifetime data set is analysed under log-gamma regression models and a model checking based on the martingale-type residual is performed.

Influence diagnostics in Birnbaum-Saunders nonlinear regression models

We consider the issue of assessing influence of observations in the class of Birnbaum-Saunders nonlinear regression models, which is useful in lifetime data analysis. Our results generalize those in Galea et al. [8] which are confined to Birnbaum-Saunders linear regression models. Some influence methods, such as the local influence, total local influence of an individual and generalized leverage are discussed. Additionally, the normal curvatures for studying local influence are derived under some perturbation schemes. We also give an application to a real fatigue data set.

Fatores associados à capacidade para o trabalho de trabalhadores do Setor Elétrico

O Setor Elétrico passou por recente processo de reestruturação produtiva com reflexos nas condições e organização do trabalho, podendo comprometer a capacidade para o trabalho. Este estudo objetivou avaliar fatores associados à capacidade para o trabalho junto a 475 trabalhadores de uma empresa do Setor Elétrico no Estado de São Paulo, Brasil. Neste estudo transversal foi realizada análise descritiva e análise de regressão linear múltipla. A média do Índice de Capacidade para o Trabalho (ICT) foi de 41,8 pontos (escala de 7,0 a 49,0 pontos). A análise múltipla mostrou que os fatores que melhor explicaram a variabilidade do ICT foram estresse no trabalho (p < 0,001) e saúde física (p < 0,001 em todas as dimensões). Em outra análise, excluídas as dimensões da saúde, as variáveis associadas ao ICT foram estresse no trabalho (p < 0,001), local de trabalho (p = 0,022), prática de atividade física (p = 0,001), consumo de álcool (p = 0,012) e índice de massa corporal (p < 0,001). Os resultados identificaram aspectos a serem considerados no desenvolvimento de medidas visando a preservação da capacidade para o trabalho, com ênfase no controle do estresse no trabalho e na promoção da saúde.

Efetividade de programa de suplementação alimentar no ganho ponderal de crianças

OBJETIVO: Avaliar a efetividade de programa governamental de suplementação alimentar no ganho ponderal de crianças. MÉTODOS: Estudo de coorte com dados secundários de 25.433 crianças de baixa renda com idade entre seis e 24 meses que ingressaram em programa de distribuição de leite fortificado Projeto Vivaleite, realizado no Estado de São Paulo de 2003 a 2008. O ganho ponderal foi medido por meio dos valores de escores z de peso para idade, calculados pelo padrão da Organização Mundial da Saúde (2007), obtidos, na rotina do programa, ao ingressar e a cada quatro meses durante a permanência. As crianças foram divididas em três grupos de escore z ao entrar: sem comprometimento de peso (z > -1); risco de baixo peso (-2 < z < -1) e baixo peso (z < -2). Utilizou-se regressão linear multinível (modelo misto), permitindo a comparação, em cada idade, das médias ajustadas do escore z dos ingressantes e participantes há pelo menos quatro meses, ajustadas para correlação entre medidas repetidas. RESULTADOS: Verificou-se efeito positivo do programa no ganho de peso das crianças, variando em função do estado nutricional ao ingressar; para as que entraram sem comprometimento de peso, o ganho médio ajustado foi 0,183 escore z;entre as que entraram com risco de baixo peso, foi 0,566; e entre as ingressantes com baixo peso, foi 1,005 escore z. CONCLUSÕES: O programa é efetivo para o ganho ponderal de crianças menores de dois anos, com efeito mais pronunciado entre as crianças que entram no programa em condições menos favoráveis de peso.

Fatores relacionados à ocorrência de leishmaniose tegumentar no Vale do Ribeira

INTRODUÇÃO: este estudo teve como objetivo identificar fatores ambientais e sociais determinantes na incidência da leishmaniose tegumentar americana no Vale do Ribeira no período de 1998 a 2006. MÉTODOS: foram utilizados dados secundários de domínio público dos 23 municípios que integram a região. O intervalo de tempo foi dividido em três períodos, pelas características gráficas dos coeficientes de incidência, os quais foram submetidos à análise por regressão linear múltipla. RESULTADOS: para o período de 1998 a 2000, as variáveis correlacionadas com a LTA foram índice de desenvolvimento humano médio (p = 0,007), renda per capita (p =0,390) e grau de urbanização (p = 0,079). No período de 2001 a 2003 e 2004 a 2006 as variáveis correlacionadas com LTA foram: a existência de flebotomíneos (p = 0,000 e p = 0,001) e a população urbana média (p = 0,007 e p = 0,001). CONCLUSÕES: esses dados demonstram a tendência de pauperização e urbanização da doença.

Influência da renda sobre as despesas com alimentação fora do domicílio, no Brasil, 2002-2003

Objetivou-se descrever e avaliar a influência da renda sobre a participação da alimentação fora do domicílio no Brasil. Utilizaram-se dados coletados pela Pesquisa de Orçamentos Familiares realizada em 2002/2003 (POF 2002/2003), pelo Instituto Brasileiro de Geografia e Estatística. Analisaram-se os registros dos gastos com aquisições de alimentos e bebidas consumidos fora do domicílio. A associação entre a participação da alimentação fora do domicílio e a renda, ajustada para atributos sócio-demográficos, foi estudada por meio de modelos de regressão utilizados para estimação de coeficientes de elasticidade-renda. A alimentação fora do domicílio representou 21% do total dos gastos com alimentação; destaque-se que o incremento de 10% na renda aumentaria em 3% a participação da alimentação fora do domicílio. O efeito da renda sobre a participação da alimentação fora, ainda que sempre positivo, diminui conforme elevação da renda, sendo alto nos domicílios com renda inferior a R$68,70 per capita/mês. Há influência da renda nos gastos com alimentação fora do domicílio, assim a evolução favorável da renda resultará em aumento dessa forma de se alimentar.

Efetividade da suplementação diária ou semanal com ferro na prevenção da anemia em lactentes

OBJETIVO: Avaliar a efetividade da suplementação universal profilática com sulfato ferroso, em administração diária ou semanal, na prevenção da anemia em lactentes. MÉTODOS: Ensaio de campo randomizado com crianças de seis a 12 meses de idade, atendidas em unidades básicas de saúde do município do Rio de Janeiro, em 2004-2005. Foram formadas três coortes concorrentes com suplementação universal com sulfato ferroso com grupos: diário (n=150; 12,5mgFe/dia), semanal (n=147; 25mgFe/semana) e controle (n=94). A intervenção durou 24 semanas e foi acompanhada por ações educativas promotoras de adesão. A concentração de hemoglobina sérica foi analisada segundo sua distribuição, média e prevalência de anemia (Hb<110,0g/L) aos 12 meses de idade. A avaliação da efetividade foi realizada segundo intenção de tratar e adesão ao protocolo, utilizando-se análises de regressão múltipla (linear e de Poisson). RESULTADOS: Os grupos mostraram-se homogêneos quanto às variáveis de caracterização. A intervenção foi operacionalizada com sucesso, com elevada adesão ao protocolo em ambos os grupos expostos a ela, sem diferença estatística entre eles. Após ajuste, somente o esquema diário apresentou efeito protetor. Na análise por adesão, o esquema diário apresentou evidente efeito dose-resposta para média de hemoglobina sérica e prevalência de anemia, não sendo observado nenhum efeito protetor do esquema semanal. CONCLUSÕES: Apenas o esquema diário de suplementação universal com sulfato ferroso dos seis aos 12 meses de idade foi efetivo em aumentar a concentração de hemoglobina sérica e em reduzir o risco de anemia

Avaliação da ingestão de alimentos por nipo-brasileiros utilizando análise fatorial

Descreve-se o uso da análise fatorial na avaliação dos hábitos alimentares de nipo-brasileiros. Utilizaram-se dados dietéticos de 1.283 participantes de estudo transversal. A partir de critérios estatísticos e do significado conceitual dos padrões identificados, geraram-se escores que definiram os perfis dietéticos (japonês ou ocidental). Empregou-se o teste t de Student pareado, os modelos de regressão linear e de Poisson para examinar as relações desses escores com, respectivamente, a geração, índice de massa corporal (IMC), perímetro abdominal e a presença de síndrome metabólica. Aqueles de primeira geração, em relação aos de segunda, apresentaram escores maiores para o perfil japonês e menores para o ocidental. O perfil ocidental relacionou-se com o IMC (p = 0,001), perímetro abdominal (p = 0,023) e a síndrome metabólica (p < 0,05). Conclui-se que os escores discriminaram sujeitos que mantêm ou não estilo de vida tradicional japonês e que a incorporação de hábitos ocidentais associou-se a maiores valores de IMC, perímetro abdominal e a presença de síndrome metabólica

Relationships of blood lead to calcium, iron, and vitamin C intakes in Brazilian pregnant women

Background & aims. This study aimed to determine the relationship between blood lead concentrations and calcium, iron and vitamin C dietary intakes of pregnant women. Methods. Included in the study were 55 women admitted to a hospital, for delivery, from June to August 2002. A food frequency questionnaire was applied to determine calcium, iron and vitamin C intakes, and a general questionnaire to obtain data on demographic-socioeconomic condition, obstetric history, smoking habit, and alcohol intake. Blood lead and haemoglobin were determined, respectively, by atomic absorption spectrometry and by the haemoglobinometer HemoCue®. Multiple linear regression models were used to determine the relationship between blood lead and calcium, iron and vitamin C intakes, and haemoglobin levels, controlling for confounders. Results. The final model of the regression analysis detected an inverse relationship between blood lead and age of the women (p=0.011), haemoglobin (p=0.001), vitamin C (p=0.012), and calcium intake (p<0.001) (R2=0.952). One hundred percent, 98.2% and 43.6% of the women were below the adequate intake (AI) for calcium, and below the recommended dietary allowances (RDA) for iron, and vitamin C, respectively. Conclusion. Despite the small sample size, the results of this study suggest that maternal age, haemoglobin, vitamin C intake, and calcium intake may interfere with blood concentrations of lead

Stress at work among electric utility workers

In the last decades there was an increase in stress at work and its effects on workers' health. These issues are still little studied in the electric utility sector. This study aims to evaluate factors associated with stress at work and to verify its associations with health status among workers of an electric company in São Paulo State, Brazil. A cross-sectional study was conducted with 474 subjects (87.5% of the eligible workers). Data were collected using self-reported questionnaires. A descriptive analysis, a multiple linear hierarchical regression analysis and a correlation analysis were performed. The majority of participants were males (91.1%) and the mean age was 37.5 yr. The mean score of stress level was 2.3 points (scale ranging from 1.0 to 5.0). Hierarchical multiple analyses showed that: regular practice of physical activities (p=0.025) and individual monthly income (p=0.002) were inversely associated with stress level; BMI was marginally associated with the stress level (p=0.074). The demographic characteristics were not associated with stress. Stress at work was significantly associated with physical and mental health status (p<0.001). To improve health of electric utility workers, actions are suggested to decrease stress by remuneration and an appropriate practice of physical activity aiming reduction of BMI

Assessing influence in survival data with a cure fraction and covariates

Diagnostic methods have been an important tool in regression analysis to detect anomalies, such as departures from error assumptions and the presence of outliers and influential observations with the fitted models. Assuming censored data, we considered a classical analysis and Bayesian analysis assuming no informative priors for the parameters of the model with a cure fraction. A Bayesian approach was considered by using Markov Chain Monte Carlo Methods with Metropolis-Hasting algorithms steps to obtain the posterior summaries of interest. Some influence methods, such as the local influence, total local influence of an individual, local influence on predictions and generalized leverage were derived, analyzed and discussed in survival data with a cure fraction and covariates. The relevance of the approach was illustrated with a real data set, where it is shown that, by removing the most influential observations, the decision about which model best fits the data is changed.

Stress at Work among Electric Utility Workers

In the last decades there was an increase in stress at work and its effects on workers' health. These issues are still little studied in the electric utility sector. This study aims to evaluate factors associated with stress at work and to verify its associations with health status among workers of an electric company in Sao Paulo State, Brazil. A cross-sectional study was conducted with 474 subjects (87.5% of the eligible workers). Data were collected using self-reported questionnaires. A descriptive analysis, a multiple linear hierarchical regression analysis and a correlation analysis were performed. The majority of participants were males (91.1%) and the mean age was 37.5 yr. The mean score of stress level was 2.3 points (scale ranging from 1.0 to 5.0). Hierarchical multiple analyses showed that: regular practice of physical activities (p=0.025) and individual monthly income (p=0.002) were inversely associated with stress level; BMI was marginally associated with the stress level (p=0.074). The demographic characteristics were not associated with stress. Stress at work was significantly associated with physical and mental health status (p<0.001). To improve health of electric utility workers, actions are suggested to decrease stress by remuneration and an appropriate practice of physical activity aiming reduction of BMI.

Espacialização da temperatura do ar anual no estado de Alagoas com diferentes modelos digitais de elevação e resoluções espaciais

The aim of this study was to establish a digital elevation model and its horizontal resolution to interpolate the annual air temperature for the Alagoas State by means of multiple linear regression models. A multiple linear regression model was adjusted to series (11 to 34 years) of annual air temperatures obtained from 28 weather stations in the states of Alagoas, Bahia, Pernambuco and Sergipe, in the Northeast of Brazil, in function of latitude, longitude and altitude. The elevation models SRTM and GTOPO30 were used in the analysis, with original resolutions of 90 and 900 m, respectively. The SRTM was resampled for horizontal resolutions of 125, 250, 500, 750 and 900 m. For spatializing the annual mean air temperature for the state of Alagoas, a multiple linear regression model was used for each elevation and spatial resolution on a grid of the latitude and longitude. In Alagoas, estimates based on SRTM data resulted in a standard error of estimate (0.57 degrees C) and dispersion (r(2) = 0.62) lower than those obtained from GTOPO30 (0.93 degrees C and 0.20). In terms of SRTM resolutions, no significant differences were observed between the standard error (0.55 degrees C; 750 m - 0.58 degrees C; 250m) and dispersion (0.60; 500 m - 0.65; 750 m) estimates. The spatialization of annual air temperature in Alagoas, via multiple regression models applied to SRTM data showed higher concordance than that obtained with the GTOPO30, independent of the spatial resolution.

Non-Cardiac Surgery in Developing Countries: Epidemiological Aspects and Economical Opportunities - The Case of Brazil

Background: Worldwide distribution of surgical interventions is unequal. Developed countries account for the majority of surgeries and information about non-cardiac operations in developing countries is scarce. The purpose of our study was to describe the epidemiological data of non-cardiac surgeries performed in Brazil in the last years. Methods and Findings: This is a retrospective cohort study that investigated the time window from 1995 to 2007. We collected information from DATASUS, a national public health system database. The following variables were studied: number of surgeries, in-hospital expenses, blood transfusion related costs, length of stay and case fatality rates. The results were presented as sum, average and percentage. The trend analysis was performed by linear regression model. There were 32,659,513 non-cardiac surgeries performed in Brazil in thirteen years. An increment of 20.42% was observed in the number of surgeries in this period and nowadays nearly 3 million operations are performed annually. The cost of these procedures has increased tremendously in the last years. The increment of surgical cost was almost 200%. The total expenses related to surgical hospitalizations were more than $10 billion in all these years. The yearly cost of surgical procedures to public health system was more than $1.27 billion for all surgical hospitalizations, and in average, U$445.24 per surgical procedure. The total cost of blood transfusion was near $98 million in all years and annually approximately $10 million were spent in perioperative transfusion. The surgical mortality had an increment of 31.11% in the period. Actually, in 2007, the surgical mortality in Brazil was 1.77%. All the variables had a significant increment along the studied period: r square (r(2)) = 0.447 for the number of surgeries (P = 0.012), r(2) = 0.439 for in-hospital expenses (P = 0.014) and r(2) = 0.907 for surgical mortality (P = 0.0055). Conclusion: The volume of surgical procedures has increased substantially in Brazil through the past years. The expenditure related to these procedures and its mortality has also increased as the number of operations. Better planning of public health resource and strategies of investment are needed to supply the crescent demand of surgery in Brazil.