149 resultados para multiple linear regression


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Endomyocardial fibrosis (EMF) is a restrictive cardiomyopathy manifested mainly by diastolic heart failure. It is recognized that diastole is an important determinant of exercise capacity. The purpose of this study was to determine whether resting echocardiographic parameters might predict oxygen consumption (VO(2p)) by ergoespirometry and the prognostic role of functional capacity in EMF patients. A total of 32 patients with biventricular EMF (29 women, 55.3 +/- 11.4 years) were studied by echocardiography and ergoespirometry. The relationship between the echocardiographic indexes and the percentage of predicted VO(2p) (%VO(2p)) was investigated by the `stepwise` linear regression analysis. The median VO(2p) was 11 +/- 3 mL/kg/min and the %VO(2p) was 53 +/- 9%. There was a correlation of %VO(2p) with an average of A` at four sites of the mitral annulus (A` peak, r = 0.471, P = 0.023), E`/A` of the inferior mitral annulus (r = -0.433, P = 0.044), and myocardial performance index (r = -0.352, P = 0.048). On multiple regression analysis, only A` peak was an independent predictor of %VO(2p) (%VO(2p)= 26.34 + 332.44 x A` peak). EMF patients with %VO(2p)< 53% had an increased mortality rate with a relative risk of 8.47. In EMF patients, diastolic function plays an important role in determining the limitations to exercise and %VO(2p) has a prognostic value.

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BACKGROUND Hypertension, a risk factor for cardiovascular diseases, and obesity are becoming a health problem in many developed and developing countries, as Brazil. Although hypertension and obesity are both closely associated, there is no universal anthropometric marker of this association. This is probably due to distinct population characteristics, and in the case of Brazil, the highly heterogeneous population. We evaluated which anthropometric measurement closely relates to high blood pressure in a sample of Brazilian factory workers. METHODS A cross-sectional study was designed. In this study, multiple logistic regression and receiver operating characteristics analysis were performed in order to obtain the precise relevance of each anthropometric measurement as a blood pressure marker. Nine hundred and thirteen men, 36 +/- 8 years-old, were submitted to a standardized questionnaire of demographic and risk factors knowledge, anthropometric and conventional blood pressure measurements were taken, and blood sample evaluations of glucose, total cholesterol, LDL-Cholesterol, and triglycerides were performed. RESULTS Overweightness or obesity was identified in 64, 11.1% were smokers and hypertension was detected in 29.2% of the participants. A linear correlation was significant (P < 0.001) between both the systolic and diastolic blood pressure and all anthropometric measurements, except for the systolic blood pressure and waist-to-hip ratio. Waist circumference (WC) was the only independent anthropometric measurement related to hypertension. Hypertensive patients presented all anthropometric measurements larger than normotensives. CONCLUSIONS Age and WC were the only independent predictors of hypertension, indicating that this simple measurement may be useful as a marker of hypertension in the Brazilian male, younger adult population. Am J Hypertens 2009; 22:980-984 (C) 2009 American Journal of Hypertension, Ltd.

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Objective To assess dietary quality and associated factors in adolescents. Study design We conducted a population-based cross-sectional study in a sample of 1584 adolescents living in areas of the state of Sao Paulo, Brazil. Dietary intake was measured with the 24-hour recall method, and dietary quality was assessed by means of the Health Eating Index (HEI), adapted to fit to the local requirements. Linear regression analyses were performed to assess the association between the HEI and demographic, socioeconomic, and lifestyle variables. Results A total of 97.1% of the adolescents studied had an inadequate diet or a diet that needed improvement. The mean overall HEI score was 59.7. Lower mean HEI scores were found for fruits, dairy products, and vegetables. Male adolescents who were physically active and lived in a house or apartment had higher HEI scores. The multiple regression analyses showed that the quality of the diet improved as age decreased. Adolescents who lived in houses or apartments had higher HEI scores than adolescents living in shacks or slums, regardless of age and energy intake. Conclusions Dietary quality is associated with income and age. A better understanding of the factors associated can provide input to the formulation of policies and development of nutritional actions. (J Pediatr 2010; 156:456-60).

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This study aimed at evaluating the thermal performance of a modular ceiling system for poultry houses. The reduced- and distorted-scale prototypes used ceiling modules made of reforested wood and were covered with recycled long-life package tiles. The following parameters were measured for 21 days: the internal surface temperature (ST), globe temperature and humidity index (WBGT), and radiant heat load (RHL). Measurements were made at times of highest heat load (11:00 am, 13:00 pm, and 03:00 pm). Collected data were analyzed by ""R"" statistics software. Means were compared by multiple comparison test (Tukey) and linear regression was performed, both at 5% significance level. The results showed that the prototype with the ceiling was more efficient to reduce internal tile surface temperature; however, this was not sufficient to provide a comfortable environment for broilers during the growout. Therefore, other techniques to provide proper cooling are required in addition to the ceiling

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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.

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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.

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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.

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This paper derives the second-order biases Of maximum likelihood estimates from a multivariate normal model where the mean vector and the covariance matrix have parameters in common. We show that the second order bias can always be obtained by means of ordinary weighted least-squares regressions. We conduct simulation studies which indicate that the bias correction scheme yields nearly unbiased estimators. (C) 2009 Elsevier B.V. All rights reserved.

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The aim of this study was to evaluate the relationship between malocclusion and self-perception of oral appearance/function, in 12/15-year-old Brazilian adolescents. The cluster sample consisted of 717 teenagers attending 24 urban public (n=611) and 5 rural public (n=107) schools in Maringá/PR. Malocclusion was measured using the Dental Aesthetic Index (DAI), in accordance with WHO recommendations. A parental questionnaire was applied to collect information on esthetic perception level and oral variables related to oral health. Univariate and multiple logistic regression analyses were performed. Multiple logistic regression confirmed that for 12-year-old, missing teeth (OR=2.865) and presence of openbite (open occlusal relationship) (OR=2.865) were risk indicators for speech capability. With regard to 15-year-old, presence of mandibular overjet (horizontal overlap) (OR=4.016) was a risk indicator for speech capability and molar relationship (OR=1.661) was a risk indicator for chewing capability. The impact of malocclusion on adolescents' life was confirmed in this study. Speech and chewing capability were associated with orthodontic deviations, which should be taken into consideration in oral health planning, to identify risk groups and improve community health services.

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The present study aimed to compare the fluoride (F-) release pattern of a nanofilled resin-modified glass ionomer cement (GIC) (Ketac N100 - KN) with available GICs used in dental practice (resin-modified GIC - Vitremer - V; conventional GIC - Ketac Molar - KM) and a nanofilled resin composite (Filtek Supreme - RC). Discs of each material (n=6) were placed into 4 mL of deionized water in sealed polyethylene vials and shaken, for 15 days. F- release (μg F-/cm²) was measured each day using a fluoride-ion specific electrode. Cumulative F- release means were statistically analyzed by linear regression analysis. In order to analyze the differences among materials and the influence of time in the daily F- release, 2-way ANOVA test was performed (α=0.05). The linear fits between the cumulative F- release profiles of RC and KM and time were weak. KN and V presented a strong relationship between cumulative F- release and time. There were significant differences between the daily F- release overtime up to the third day only for GICs materials. The daily F- release means for RC were similar overtime. The results indicate that the F- release profile of the nanofilled resin-modified GIC is comparable to the resin-modified GIC.

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A retrospective survey was designed to identify diagnostic subgroups and clinical factors associated with odontogenic pain and discomfort in dental urgency patients. A consecutive sample of 1,765 patients seeking treatment for dental pain at the Urgency Service of the Dental School of the Federal University of Goiás, Brazil, was selected. Inclusion criteria were pulpal or periapical pain that occurred before dental treatment (minimum 6 months after the last dental appointment), and the exclusion criteria were teeth with odontogenic developmental anomalies and missing information or incomplete records. Clinical and radiographic examinations were performed to assess clinical presentation of pain complaints including origin, duration, frequency and location of pain, palpation, percussion and vitality tests, radiographic features, endodontic diagnosis and characteristics of teeth. Chi-square test and multiple logistic regression were used to analyze association between pulpal and periapical pain and independent variables. The most frequent endodontic diagnosis of pulpal pain were symptomatic pulpitis (28.3%) and hyperreactive pulpalgia (14.4%), and the most frequent periapical pain was symptomatic apical periodontitis of infectious origin (26.4%). Regression analysis revealed that closed pulp chamber and caries were highly associated with pulpal pain and, conversely, open pulp chamber was associated with periapical pain (p<0.001). Endodontic diagnosis and local factors associated with pulpal and periapical pain suggest that the important clinical factor of pulpal pain was closed pulp chamber and caries, and of periapical pain was open pulp chamber.

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The objective of this study was to compare the completion rates and performance of the Brazilian version of the Oral Health Impact Profile (OHIP14) when applied as an interview or in its original self-reported form. A convenience sample of 74 adult patients was selected in a Dental Clinic (University of Araras, Brazil). One examiner administered the instrument in both formats to participants with an interval of 2 weeks between each administration. Data about dental health condition and socioeconomic status were collected and associated with total OHIP14 scores in both formats using linear regression analyses. No differences were found in the total scores and in each subscale of the OHIP14 according to the form of administration. Higher values of completion were found in the interview format. More severe impacts were recorded in the interview format than in the questionnaire format. Higher values of total OHIP-14 scores in both formats were related to the presence of dental caries. Total OHIP14 scores were not influenced by the method of administration. However, the use of the OHIP14 in the questionnaire format may result in lower completion rates and loss of data.

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Estimou-se a prevalência de dor nos dentes e gengivas e fatores associados em adolescentes brasileiros de 15 a 19 anos de idade. Foram utilizadas informações de 16.126 adolescentes participantes do levantamento epidemiológico nacional de saúde bucal - SB Brasil 2002-2003. O desfecho foi o relato de dor nos dentes e gengivas nos últimos seis meses. As variáveis exploratórias foram: renda per capita, escolaridade, condição de estudo, sexo, cor da pele, idade, localização geográfica da residência, tipo de serviço odontológico utilizado pela última vez, tempo decorrido da última consulta odontológica, índice CPO-D e seus componentes, cálculo dentário e o índice de estética dental. Foram realizadas análises brutas e múltiplas utilizando a regressão de Poisson. A prevalência da dor de dentes e gengivas foi de 35,6% (IC95%: 34,8-36,4). A prevalência de dor foi maior nas meninas, naqueles pertencentes a famílias com baixa renda per capita, nos não estudantes e estudantes de escola pública e naqueles com baixa escolaridade para a idade. Indivíduos que apresentaram altos níveis de cárie e cálculo dentário também apresentaram maiores prevalências do desfecho. A dor nos dentes e gengivas em adolescentes pode ser considerada um problema relevante em saúde pública sugerindo a necessidade de ações preventivas e de promoção da saúde.

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The purpose of this study was to develop and validate equations to estimate the aboveground phytomass of a 30 years old plot of Atlantic Forest. In two plots of 100 m², a total of 82 trees were cut down at ground level. For each tree, height and diameter were measured. Leaves and woody material were separated in order to determine their fresh weights in field conditions. Samples of each fraction were oven dried at 80 °C to constant weight to determine their dry weight. Tree data were divided into two random samples. One sample was used for the development of the regression equations, and the other for validation. The models were developed using single linear regression analysis, where the dependent variable was the dry mass, and the independent variables were height (h), diameter (d) and d²h. The validation was carried out using Pearson correlation coefficient, paired t-Student test and standard error of estimation. The best equations to estimate aboveground phytomass were: lnDW = -3.068+2.522lnd (r² = 0.91; s y/x = 0.67) and lnDW = -3.676+0.951ln d²h (r² = 0.94; s y/x = 0.56).

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Este estudo teve como objetivo desenvolver modelos preditores de fitomassa epigéa da vegetação arbórea da Floresta Baixa de Restinga. Foram selecionadas 102 árvores de 29 espécies ocorrentes na área de estudo e 102 indivíduos de jerivá (Syagrus romanzoffiana (Cham.) Glassman), distribuídos proporcionalmente entre as classes de diâmetro da vegetação arbórea. As árvores foram cortadas, ao nível do solo e foram medidos a altura total e o diâmetro à altura do peito (DAP) de cada árvore. As folhas foram separadas do lenho e a massa fresca da porção lenhosa e foliar medidas separadamente. Amostras de cada fração foram secas a 70 °C, até peso constante, para determinação da massa seca das árvores. Os modelos foram desenvolvidos através de análise de regressão linear, sendo a variável dependente a massa seca (MS) das árvores e as variáveis independentes a altura (h), o diâmetro a altura do peito (d) e as relações d² h e d² h multiplicada pela densidade da madeira (ρ d² h). Os modelos desenvolvidos indicam que o diâmetro explica grande parte da variabilidade da fitomassa das árvores da restinga e a altura é a variável explanatória da equação específica para o jerivá. Os modelos selecionados foram: ln MS (kg) = -1,352 + 2,009 ln d (R² = 0,96; s yx = 0,34) para a comunidade vegetal sem jerivá, ln MS (kg) = -2,052 + 0,801 ln d² h (R² = 0,94; s yx = 0,38) para a comunidade incluindo o jerivá, e ln MS (kg) = -0,884 + 2,40 ln h (R² = 0,92; s yx = 0,49) para o jerivá.