ABSTRACT
Beta regressions are commonly used with responses that assume values in the standard unit interval, such as rates, proportions and concentration indices. Hypothesis testing inferences on the model parameters are typically performed using the likelihood ratio test. It delivers accurate inferences when the sample size is large, but can otherwise lead to unreliable conclusions. It is thus important to develop alternative tests with superior finite sample behavior. We derive the Bartlett correction to the likelihood ratio test under the more general formulation of the beta regression model, i.e. under varying precision. The model contains two submodels, one for the mean response and a separate one for the precision parameter. Our interest lies in performing testing inferences on the parameters that index both submodels. We use three Bartlett-corrected likelihood ratio test statistics that are expected to yield superior performance when the sample size is small. We present Monte Carlo simulation evidence on the finite sample behavior of the Bartlett-corrected tests relative to the standard likelihood ratio test and to two improved tests that are based on an alternative approach. The numerical evidence shows that one of the Bartlett-corrected typically delivers accurate inferences even when the sample is quite small. An empirical application related to behavioral biometrics is presented and discussed.
Subject(s)
Biometry , Computer Simulation , Models, Biological , Models, Statistical , Data Interpretation, Statistical , Sample SizeABSTRACT
Regression analyses are commonly performed with doubly limited continuous dependent variables; for instance, when modeling the behavior of rates, proportions and income concentration indices. Several models are available in the literature for use with such variables, one of them being the unit gamma regression model. In all such models, parameter estimation is typically performed using the maximum likelihood method and testing inferences on the model's parameters are usually based on the likelihood ratio test. Such a test can, however, deliver quite imprecise inferences when the sample size is small. In this paper, we propose two modified likelihood ratio test statistics for use with the unit gamma regressions that deliver much more accurate inferences when the number of data points in small. Numerical (i.e. simulation) evidence is presented for both fixed dispersion and varying dispersion models, and also for tests that involve nonnested models. We also present and discuss two empirical applications.
ABSTRACT
Andiroba (Carapa guianensis) seeds are the source of an oil with a wide range of biological activities and ethnopharmacological uses. However, few studies have devoted attention to innovative formulations, including nanoemulsions. The present study aimed to obtain a colloidal system with the andiroba oil using a low-energy and organic-solvent-free method. Moreover, the preliminary residual larvicidal activity of the nanoemulsion against Aedes aegypti was evaluated. Oleic and palmitic acids were the major fatty acids, in addition to the phytosterol ß-sitosterol and limonoids (tetranortriterpenoids). The required hydrophile-lipophile was around 11.0 and the optimal nanoemulsion was obtained using polysorbate 85. The particle size distribution suggested the presence of small droplets (mean diameter around 150 nm) and low polydispersity index (around 0.150). The effect of temperature on particle size distribution revealed that no major droplet size increase occurred. The preliminary residual larvicidal assay suggested that the mortality increased as a function of time. The present study allowed achievement of a potential bioactive oil in water nanoemulsion that may be a promising controlled release system. Moreover, the ecofriendly approach involved in the preparation associated with the great bioactive potential of C. guianensis makes this nanoemulsion very promising for valorization of this Amazon raw material.
ABSTRACT
Apresenta o Projeto Memória da Psiquiatria no Brasil, fruto da cooperaçÝo entre o Departamento de Arquivo e DocumentaçÝo da Casa de Oswaldo Cruz e o Núcleo de Estudos Político-Sociais em Saúde da Escola Nacional de Saúde Pública. Lista, em seguida, 97 títulos de periódicos nÝo correntes relativos à psiquiatria e à saúde mental, integrantes do acervo da Biblioteca de Manguinhos. Deste conjunto dá especial destaque ao Boletim de Eugenia.(MAM)
Subject(s)
Periodical , Psychiatry/history , Public Health/history , Brazil , Mental Health , Syzygium/historyABSTRACT
Apresenta o Projeto Memória da Psiquiatria no Brasil, fruto da cooperaçäo entre o Departamento de Arquivo e Documentaçäo da Casa de Oswaldo Cruz e o Núcleo de Estudos Político-Sociais em Saúde da Escola Nacional de Saúde Pública. Lista, em seguida, 97 títulos de periódicos näo correntes relativos à psiquiatria e à saúde mental, integrantes do acervo da Biblioteca de Manguinhos. Deste conjunto dá especial destaque ao Boletim de Eugenia.(MAM)