Estimation in nonlinear mixed-effects models using heavy-tailed distributions

Nonlinear mixed-effects models are very useful to analyze repeated measures data and are used in a variety of applications. Normal distributions for random effects and residual errors are usually assumed, but such assumptions make inferences vulnerable to the presence of outliers. In this work, we introduce an extension of a normal nonlinear mixed-effects model considering a subclass of elliptical contoured distributions for both random effects and residual errors. This elliptical subclass, the scale mixtures of normal (SMN) distributions, includes heavy-tailed multivariate distributions, such as Student-t, the contaminated normal and slash, among others, and represents an interesting alternative to outliers accommodation maintaining the elegance and simplicity of the maximum likelihood theory. We propose an exact estimation procedure to obtain the maximum likelihood estimates of the fixed-effects and variance components, using a stochastic approximation of the EM algorithm. We compare the performance of the normal and the SMN models with two real data sets.     

A parameter expansion version of the SAEM algorithm

The EM algorithm and its extensions are very popular tools for maximum likelihood estimation in incomplete data setting. However, one of the limitations of these methods is their slow convergence. The PX-EM (parameter-expanded EM) algorithm was proposed by Liu, Rubin and Wu to make EM much faster. On the other hand, stochastic versions of EM are powerful alternatives of EM when the E-step is untractable in a closed form. In this paper we propose the PX-SAEM which is a parameter expansion version of the so-called SAEM (Stochastic Approximation version of EM). PX-SAEM is shown to accelerate SAEM and improve convergence toward the maximum likelihood estimate in a parametric framework. Numerical examples illustrate the behavior of PX-SAEM in linear and nonlinear mixed effects models.     

Monitoring and modeling the urban growth of two mid-sized Chilean cities

Chile's economic development model changed drastically in 1973. Public policy liberalization ended and the market became the principal entity for regulating growth, including urban growth. The implementation of this new model resulted in unprecedented urban growth, markedly impacting the landscape. In mid-sized cities, this spatial growth has been especially significant. Two examples of such mid-sized cities are Chillán and Los Ángeles, located in the Biobío Region, in the so-called Central Valley. This research analyzed the land use/cover change in Chillán and Los Ángeles from 1978 to 1998, identified the patterns of urban growth and the fragmentation of the urban space, applying GIS and remote sensing tools. The main driving forces of the urban changes were analyzed and the model to predict the land use/cover changes was applied. Our results show the importance of monitoring and modeling rapid urban growth for attaining sustainable mid-sized cities in developing countries that are strongly dependent on export of natural resources. Monitoring and modeling could also help to avoid a repetition of the errors that produced the unsustainable growth characteristic of large Latin American cities.     

Disciplinary intersections of gender and ethnicity in populist radical right media in Romania

The present study examines how the desirable ideals of femininity for the ethno-nationalist project are framed in populist radical right media in contemporary Romania. The study examines the editorials of populist radical right party leader (Corneliu Vadim Tudor) published at election times between 2000 and 2012 in the weekly party publication. It explores the inventory of media frames, which provide the panopticon of femininity performances coming forth in Tudor’s editorials, and the disciplining endeavours these depictions enable. In the first step, the femininity performance of Romanian women seen as nationalist ideal of submission and childbearing is juxtaposed with the portrayal of women who forsake such expectations, and that of Roma women described as promiscuous and overly fertile. In the second step, the roles afforded to women in the public arena are evidenced, either as selfless heroines or their antithetic depiction, the power-hungry women.     

Promoting Development in Weak Institutional Environments: The Understanding and Transmission of Sustainability by NGOS in Latin America

Non-governmental organizations (NGOs) are a major institutional force in promoting sustainable development, especially in institutional environments where governments have often not been able to assume the role of development agent. Despite this importance, the approach of Latin American NGOs to sustainability has received only little attention so far and respective research is scarce. To address this research gap, we conducted an online survey of 306 Latin American NGOs, investigating their understanding of sustainability and how they seek to transmit it. Due to the lack of previous empirical studies, our study is exploratory in nature and examines eight research categories: (1) NGOs definition of sustainability; (2) the role they see for themselves in its promotion, (3) dimensions of sustainability judged as important, (4) stakeholders and (5) partners considered, (6) motives for pursuing sustainability, (7) forms of implementation, and (8) measures regarded as necessary for spreading it further. Our findings are discussed against the institutional environment of Latin America, as we assume that the understanding and transmission of sustainability is contextual in nature. Our study shows that the sustainability concept of the sample NGOs is broad and that they take a wide variety of efforts for implementing it. Exploratory and confirmatory factor analyses confirmed the reliability and validity of the eight-component-model we applied for our study. Thus, it serves as a valuable starting point for future research into the “terra incognita” of Latin American NGOs’ approach to sustainability.     

Tolerance Toward Immigrants as a Dimension of Cosmopolitanism: Explaining Attitudes Toward Immigrants in Houston

Tolerance toward immigrants can be explained as the development of dispositions toward the acceptance of foreigners as locals influenced by the city’s multicultural contexts. Accordingly, tolerance toward immigrants represents a dimension of cosmopolitanism in metropolitan areas of receiving societies. In this study, I examine whether the proportion of immigrants in communities is directly associated with tolerance toward immigrants and whether there are significant differences in attitudes toward immigrants by occupation and educational attainment in the metropolitan research setting of Houston, Texas. Using data from the Houston Area Survey, I find that the percentage of foreign born in census tracts is directly associated with tolerance, that white-collar workers are not more tolerant than non-white-collar workers, and that the effect of education on tolerance toward immigrants is not always positive. I conclude that, in Houston, tolerance toward immigrants represents a dimension of cosmopolitanism, and cosmopolitanism is not well founded on socioeconomic status.     

Validation of the Satisfaction with Life Scale to Brazilians: Evidences of Measurement Noninvariance Across Brazil and US

Satisfaction with life is one of three hallmarks of subjective well-being, along with frequent positive emotions and infrequent negative emotions (Diener et al. in Psychol Bull 125:276–302, 1999), and the satisfaction with life scale (SWLS; Diener et al. in J Pers Assess 49:91–95, 1985) has been used worldwide to evaluate it. The current study seeks to (a) adapt and gather evidence of validity and reliability of the SWLS for a Brazilian sample, (b) evaluate gender equivalence on Brazilian university students, and (c) test for invariance between Brazilian and US samples. Participants were US (N = 241), and Brazilian (N = 1,388) undergraduates. Results from the Brazilian sample, based on confirmatory factor analyses and measurement invariance tests, showed: (a) evidence of validity of the scale, (b) scalar invariance across gender, (c) scalar invariance within group. However, nonequivalence between Brazil and US samples was found. Such results suggest that within comparisons can be conducted with Brazilian undergraduates, but comparisons between Brazil and the US might be misleading due to lack of invariance. Similar findings have already been reported in other cultures and raise questions about cross cultural studies with this scale.