Mixed Models Research Papers - Academia.edu (original) (raw)

Mixed mode four-point testing is performed on polyurethane foams. This paper presents only the results on the stress intensity factors (SIFs) obtained experimentally for a density of 325 kg/m 3 , although tests were done for three foam... more

Mixed mode four-point testing is performed on polyurethane foams. This paper presents only the results on the stress intensity factors (SIFs) obtained experimentally for a density of 325 kg/m 3 , although tests were done for three foam densities. An asymmetric four-point bending setup was used for determining the critical SIFs in Mode I and Mode II, and discussions on the influence of the initial crack length on the SIF values are done. As initial crack length is increased the theoretical predictions give a better comparison to experimentally obtained results.

The author presents a method of hierarchical bayesian estimation to estimate the value of the different income variables on the basis of studies of household budgets and POLTAX tax register. Calculations have been made for the case where... more

The author presents a method of hierarchical bayesian estimation to estimate the value of the different income variables on the basis of studies of household budgets and POLTAX tax register. Calculations have been made for the case where approximately known a priori evaluation of hyperparameters used to construct a conditional probability, which is used in the model. The author compares the efficiency of the estimates obtained by using other hierarchical methods of estimation for small areas, including the EBLUP estimators type. This gave congruity in precision of the estimated parameters using both techniques.

Information about the diameter distribution of a forest stand is an essential component for deriving a variety of stand attributes, understanding stand dynamics under varying ecological conditions and planning future forest prescriptions.... more

Information about the diameter distribution of a forest stand is an essential component for deriving a variety of stand attributes, understanding stand dynamics under varying ecological conditions and planning future forest prescriptions. Diameter distributions from multiple even-aged stands of Pinus occidentalis from three different ecological zones within La Sierra region in the Dominican Republic were modeled using a three-parameter Weibull probability prediction method using either maximum likelihood or modified method of moments, and two bases on parameter recovery method using either percentile-based or cumulative distribution function regression. Stand characteristics such as age, total tree height, trees per hectare, site quality and basal area were employed as predictor variables. Methods were evaluated based on goodnessof-
fit of the distributions and RMSE of stand yield. In these data, the parameter recovery method based on percentile based distribution proved to be considerably more efficient in describing the diameter distribution.

Ecology Letters (2010) 13: 728–735Ecology Letters (2010) 13: 728–735AbstractThe metabolic theory of ecology links physiology with ecology, and successfully predicts many allometric scaling relationships. In recent years, proponents and... more

Ecology Letters (2010) 13: 728–735Ecology Letters (2010) 13: 728–735AbstractThe metabolic theory of ecology links physiology with ecology, and successfully predicts many allometric scaling relationships. In recent years, proponents and critics of metabolic theory have debated vigorously about the scaling of metabolic rate. We show that the controversy arose, in part, because researchers examined the mean exponent separately from the variance. We estimate both quantities simultaneously using linear mixed-effects models and data from 1242 animal species. Metabolic rate scaling converges on the predicted value of 3/4 but is highly heterogeneous: 50% of orders lie outside the range 0.68–0.82. These findings are robust to several forms of statistical uncertainty. We then test competing hypotheses about the variation. Metabolic theory is currently unable to explain differences in scaling among orders, but the patterns are not consistent with competing explanations either. We conclude that current theories are inadequate to explain the full range of metabolic scaling patterns observed in nature.The metabolic theory of ecology links physiology with ecology, and successfully predicts many allometric scaling relationships. In recent years, proponents and critics of metabolic theory have debated vigorously about the scaling of metabolic rate. We show that the controversy arose, in part, because researchers examined the mean exponent separately from the variance. We estimate both quantities simultaneously using linear mixed-effects models and data from 1242 animal species. Metabolic rate scaling converges on the predicted value of 3/4 but is highly heterogeneous: 50% of orders lie outside the range 0.68–0.82. These findings are robust to several forms of statistical uncertainty. We then test competing hypotheses about the variation. Metabolic theory is currently unable to explain differences in scaling among orders, but the patterns are not consistent with competing explanations either. We conclude that current theories are inadequate to explain the full range of metabolic scaling patterns observed in nature.

Increasing global competition demands that the manufacturing industry move from mass production into mass customization production in order to provide more varieties of products and thus satisfy customer demands. It has been shown that... more

The main purpose of the study was to examine the changes in the average academic performance of students over time and how these changes are related to student segments, choice of program and the entry qualification of the student. The... more

The main purpose of the study was to examine the changes in the average academic performance of students over time and how these changes are related to student segments, choice of program and the entry qualification of the student. The cohort of students admitted into Bolgatanga Polytechnic during the 2009/2010 academic year formed the sample and only students who successfully completed were used. Data on grade point averages (GPA), demographic and socio-economic features from 131 Female and 271 Male students was obtained from the Examinations Department and the Student Affairs Unit of Bolgatanga Polytechnic. The multivariate analysis of variance technique was used to complement the Hotelling’s T 2 to compare the mean vectors of k random samples for significant difference among the levels of Departments, Entry Requirements and Gender. Profile analysis of the data indicated at 5 % level of significance that the average GPA scores of the Male and Female students were parallel, level a...

Con el objetivo de evaluar la equidad de género dentro del estudio de la calidad de la democracia, se realiza un análisis del nivel de igualdad para las mujeres y hombres en materia de educación y trabajo en el Perú. Mediante el Análisis... more

Con el objetivo de evaluar la equidad de género dentro del estudio de la calidad de la democracia, se realiza un análisis del nivel de igualdad para las mujeres y hombres en materia de educación y trabajo en el Perú. Mediante el Análisis de Componentes Principales, la comparación de valores medios y la elaboración de modelos mixtos de efectos aleatorios se ha comprobado y cuantificado si ser mujer tiene una influencia significativa sobre los valores de cada una de las variables seleccionadas en los años 2008 y 2018. Se concluye que la desigualdad de género es uno de los principales problemas de la democracia en el Perú, es decir, el género es determinante para medir la calidad de la democracia. With the aim of evaluating gender equality within the study of the quality of democracy, an analysis of the level of equality for women and men in education and work in Peru has been carried out. Through the Principal Component Analysis, the comparison of mean values and the elaboration of mi...

Identifying how physiological responses are structured across environmental gradients is critical to understanding in what manner ecological factors determine tree performance. Here, we investigated the spatiotemporal patterns of signal... more

Identifying how physiological responses are structured across environmental gradients is critical to understanding in what manner ecological factors determine tree performance. Here, we investigated the spatiotemporal patterns of signal strength of carbon isotope discrimination (Δ(13)C) and oxygen isotope composition (δ(18)O) for three deciduous oaks (Quercus faginea (Lam.), Q. humilis Mill. and Q. petraea (Matt.) Liebl.) and one evergreen oak (Q. ilex L.) co-occurring in Mediterranean forests along an aridity gradient. We hypothesized that contrasting strategies in response to drought would lead to differential climate sensitivities between functional groups. Such differential sensitivities could result in a contrasting imprint on stable isotopes, depending on whether the spatial or temporal organization of tree-ring signals was analysed. To test these hypotheses, we proposed a mixed modelling framework to group isotopic records into potentially homogeneous subsets according to taxonomic or geographical criteria. To this end, carbon and oxygen isotopes were modelled through different variance-covariance structures for the variability among years (at the temporal level) or sites (at the spatial level). Signal-strength parameters were estimated from the outcome of selected models. We found striking differences between deciduous and evergreen oaks in the organization of their temporal and spatial signals. Therefore, the relationships with climate were examined independently for each functional group. While Q. ilex exhibited a large spatial dependence of isotopic signals on the temperature regime, deciduous oaks showed a greater dependence on precipitation, confirming their higher susceptibility to drought. Such contrasting responses to drought among oak types were also observed at the temporal level (interannual variability), with stronger associations with growing-season water availability in deciduous oaks. Thus, our results indicate that Mediterranean deciduous and evergreen oaks constitute two clearly differentiated functional groups in terms of their carbon and water economies, despite co-existing in a wide range of environments. In contrast, deciduous oaks form a rather homogeneous group in terms of climate sensitivity.

This paper proposes a new model-based approach to estimate small areas that extends the Fay–Herriot methodology. The new model is additive, with a random term to characterize the inter-area variability and a nonparametric mean function... more

This paper proposes a new model-based approach to estimate small areas that extends the Fay–Herriot methodology. The new model is additive, with a random term to characterize the inter-area variability and a nonparametric mean function specification, defined using the information on an auxiliary variable. The most significant advantage of the proposal is that it avoids the model misspecification problem. The monotonicity is the only assumption about the functional form of the relationship between the variable of interest and the auxiliary one. Estimators for the area means are derived combining “Order Restricted Inference” and standard mixed model approaches. A large simulation experiment shows how the new approach outperforms the Fay–Herriot methodology in many scenarios. Besides, the new method is applied to the Australian farms data.

This paper aims at classifying, on the basis of their disability profile, the population of elderly and quantifying the number of those with a very low level of functioning in a central region of Italy. This is accomplished using a set of... more

This paper aims at classifying, on the basis of their disability profile, the population of elderly and quantifying the number of those with a very low level of functioning in a central region of Italy. This is accomplished using a set of variables on the difficulty of accomplishing everyday tasks (Activities of Daily Living, ADL) and functions. This issue is

This study evaluates the effects of socio-economic, demographic and geographic indicators on the malaria rapid diagnosis test (RDT), using the baseline malaria indicator survey of 2007. This survey covered the Amhara, Oromiya and Southern... more

This study evaluates the effects of socio-economic, demographic and geographic indicators on the malaria rapid diagnosis test (RDT), using the baseline malaria indicator survey of 2007. This survey covered the Amhara, Oromiya and Southern Nations, Nationalities, and People’s Region (SNNPR) of Ethiopia. A total of 224 clusters of, on average, 25 households each were selected. In total, 28,994 individuals participated in the survey. A generalized linear mixed model was used to analyze the data where the response variable was the presence or absence of malaria using the RDT. The results showed that for households with toilet facilities, clean drinking water and more living space, the chances of testing positive for malaria RDT decreased. Moreover, using malaria nets and spraying the house walls with anti-mosquito were found to be effective control measures. Key words: Cluster sampling, interaction effect, mixed model, odds ratio, rapid diagnostic test.

In this paper, we test the hypothesis that computer use will lead to productivity gains only if the firm uses an appropriate set of organizational practices. Detailed data on organizational practices and workers’ compensation are obtained... more

In this paper, we test the hypothesis that computer use will lead to productivity gains only if the firm uses an appropriate set of organizational practices. Detailed data on organizational practices and workers’ compensation are obtained through a Canadian longitudinal linked employer-employee database called the Workplace and Employee Survey (WES). Linked data allow us to take into account both worker and firm unobserved heterogeneity through the estimation of a linear mixed model of wage determination. Our results suggest a small but positive computer-wage premium whose size is related to a set of organizational practices.

La clasificacion de rodales mediante "curvas de indice de sitio" es util en el establecimiento y manejo de plantaciones forestales ya que de la calidad del sitio depende en gran parte el crecimiento y rendimiento de las mismas.... more

La clasificacion de rodales mediante "curvas de indice de sitio" es util en el establecimiento y manejo de plantaciones forestales ya que de la calidad del sitio depende en gran parte el crecimiento y rendimiento de las mismas. La mayor parte de los datos forestales son obtenidos longitudinalmente en el mismo sitio y las varianzas a menudo cambian en el tiempo, lo que hace inapropiada la aplicacion del modelo general ordinario. Los modelos mixtos son buenas alternativas al permitir modelar estructuras covariantes. En este estudio se utilizaron modelos lineales y no lineales para analizar la relacion de la altura mayor con la edad en plantaciones de Eucalyptus urophylla en Venezuela, y hallar la "curva guia" mas apropiada para la clasificacion de sitios. Los datos consistieron en mediciones repetidas obtenidas a partir de parcelas permanentes. Los modelos ajustados fueron los de Schumacher (lineal), Chapman-Richards, Weibull, Logistica, Gompertz y el Monomolecular...