ABSTRACT
We introduce a new class of heteroscedastic partially linear model (PLM) with skew-normal distribution. Maximum likelihood estimation of the model parameters by the ECM algorithm (Expectation/Conditional Maximization) as well as influence diagnostics for the new model are investigated. In addition, a Likelihood Ratio test for assessing the homogeneity of the scale parameter is presented. Simulation studies for assessing the performance of the ECM algorithm and the Likelihood Ratio test statistics for homogeneity of variance are developed. Also, a study for misspecification of the structure function is considered. Finally, an application of the new heteroscedastic PLM to a real data set on ragweed pollen concentration is presented to show that it provides a better fit than the classic homocedastic PLM. We hope that the proposed model may attract applications in different areas of knowledge.
ABSTRACT
A special source of difficulty in the statistical analysis is the possibility that some subjects may not have a complete observation of the response variable. Such incomplete observation of the response variable is called censoring. Censorship can occur for a variety of reasons, including limitations of measurement equipment, design of the experiment, and non-occurrence of the event of interest until the end of the study. In the presence of censoring, the dependence of the response variable on the explanatory variables can be explored through regression analysis. In this paper, we propose to examine the censorship problem in context of the class of asymmetric, i.e., we have proposed a linear regression model with censored responses based on skew scale mixtures of normal distributions. We develop a Monte Carlo EM (MCEM) algorithm to perform maximum likelihood inference of the parameters in the proposed linear censored regression models with skew scale mixtures of normal distributions. The MCEM algorithm has been discussed with an emphasis on the skew-normal, skew Student-t-normal, skew-slash and skew-contaminated normal distributions. To examine the performance of the proposed method, we present some simulation studies and analyze a real dataset.
ABSTRACT
The objective was evaluating the psychometric properties of the Sociocultural Attitudes Towards Appearance Questionnaire-3 (SATAQ-3) among Brazilian young adults of both genders. The sample was composed by 506 undergraduate students (295 females and 211 males), aged between 17 and 29 years old. Exploratory and confirmatory factor analyses were used for construct validity (N = 506). Correlations between the SATAQ-3 scores and those of the Tripartite Influence Scale (TIS) and Body Shape Questionnaire (BSQ) were used for convergent validity. Reliability was assessed through internal consistency (α) and reproducibility (test-retest) through comparison of the means obtained at two different time points and through intra-class correlation. The scale presented a factor structure composed of five factors, replicated in the confirmatory factor analysis with satisfactory values for the measurements of adjustment to the model. Correlations with the BSQ and TIS scores were rho = .52 and rho = -.35, respectively. Cronbach's alpha coefficients were satisfactory, and their stability was demonstrated. Brazilian SATAQ-3 had good validity and reproducibility, being indicated for use in samples of Brazilian youths.
Subject(s)
Attitude/ethnology , Body Image , Surveys and Questionnaires/standards , Adolescent , Adult , Brazil/ethnology , Factor Analysis, Statistical , Female , Humans , Male , Psychometrics/instrumentation , Reproducibility of Results , Young AdultABSTRACT
The objective was evaluating the psychometric properties of the Sociocultural Attitudes Towards Appearance Questionnaire-3 (SATAQ-3) among Brazilian young adults of both genders. The sample was composed by 506 undergraduate students (295 females and 211 males), aged between 17 and 29 years old. Exploratory and confirmatory factor analyses were used for construct validity (N = 506). Correlations between the SATAQ-3 scores and those of the Tripartite Influence Scale (TIS) and Body Shape Questionnaire (BSQ) were used for convergent validity. Reliability was assessed through internal consistency (α) and reproducibility (test-retest) through comparison of the means obtained at two different time points and through intra-class correlation. The scale presented a factor structure composed of five factors, replicated in the confirmatory factor analysis with satisfactory values for the measurements of adjustment to the model. Correlations with the BSQ and TIS scores were rho = .52 and rho = -.35, respectively. Cronbach's alpha coefficients were satisfactory, and their stability was demonstrated. Brazilian SATAQ-3 had good validity and reproducibility, being indicated for use in samples of Brazilian youths (AU)
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