On Developing Ridge Regression Parameters: A Graphical investigation

In this paper we have reviewed some existing and proposed some new estimators for estimating the ridge parameter k . All in all 19 different estimators have been studied. The investigation has been carried out using Monte Carlo simulations. A large number of different models were investigated where the variance of the random error, the number of variables included in the model, the correlations among the explanatory variables, the sample size and the unknown coefficients vectors b have been varied. For each model we have performed 2000 replications and presented the results both in term of figures and tables. Based on the simulation study, we found that increasing the number of correlated variable, the variance of the random error and increasing the correlation between the independent variables have negative effect on the MSE. When the sample size increases the MSE decreases even when the correlation between the independent variables and the variance of the random error are large. In all situations, the proposed estimators have smaller MSE than the ordinary least squared and some other existing estimators

On developing ridge regression parameters : a graphical investigation

In this paper we review some existing and propose some new estimators for estimating the ridge parameter. All in all 19 different estimators have been studied. The investigation has been carried out using Monte Carlo simulations. A large number of different models have been investigated where the variance of the random error, the number of variables included in the model, the correlations among the explanatory variables, the sample size and the unknown coefficient vector were varied. For each model we have performed 2000 replications and presented the results both in term of figures and tables. Based on the simulation study, we found that increasing the number of correlated variable, the variance of the random error and increasing the correlation between the independent variables have negative effect on the mean squared error. When the sample size increases the mean squared error decreases even when the correlation between the independent variables and the variance of the random error are large. In all situations, the proposed estimators have smaller mean squared error than the ordinary least squares and other existing estimators

Erratum to: The study of cardiovascular risk in adolescents – ERICA: rationale, design and sample characteristics of a national survey examining cardiovascular risk factor profile in Brazilian adolescents

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A Genome-Wide RNAi Screen Identifies Regulators of Cholesterol-Modified Hedgehog Secretion in Drosophila

Hedgehog (Hh) proteins are secreted molecules that function as organizers in animal development. In addition to being palmitoylated, Hh is the only metazoan protein known to possess a covalently-linked cholesterol moiety. The absence of either modification severely disrupts the organization of numerous tissues during development. It is currently not known how lipid-modified Hh is secreted and released from producing cells. We have performed a genome-wide RNAi screen in Drosophila melanogaster cells to identify regulators of Hh secretion. We found that cholesterol-modified Hh secretion is strongly dependent on coat protein complex I (COPI) but not COPII vesicles, suggesting that cholesterol modification alters the movement of Hh through the early secretory pathway. We provide evidence that both proteolysis and cholesterol modification are necessary for the efficient trafficking of Hh through the ER and Golgi. Finally, we identified several putative regulators of protein secretion and demonstrate a role for some of these genes in Hh and Wingless (Wg) morphogen secretion in vivo. These data open new perspectives for studying how morphogen secretion is regulated, as well as provide insight into regulation of lipid-modified protein secretion

Anemia em gestantes brasileiras antes e após a fortificação das farinhas com ferro

OBJECTIVE: To compare prevalence of anemia and hemoglobin (Hb) levels in Brazilian pregnant women before and after flour fortification with iron. METHODS: A repeated cross-sectional panel study of public health care centers of municipalities in the five Brazilian regions was conducted. Retrospective data were obtained from 12,119 medical records of pregnant women distributed in two groups: before fortification (delivery prior to June 2004) and after fortification (date of last period after June 2005). Anemia was defined as HbOBJETIVO: Comparar prevalencia de anemia y valores de hemoglobina (Hb) en gestantes brasileñas, antes y después de la fortificación de las harinas con hierro. MÉTODOS: Estudio de evaluación de paneles repetidos, desarrollado en servicios públicos de salud de municipios de las cinco regiones brasileñas. Datos retrospectivos se obtuvieron de 12.119 prontuarios de gestantes distribuidas en dos grupos: antes de la fortificación, con parto anterior a junio de 2004, y posterior a la fortificación, con última menstruación después de junio 2005. Anemia fue definida como HbOBJETIVO: Comparar prevalência de anemia e valores de hemoglobina (Hb) em gestantes brasileiras, antes e após a fortificação das farinhas com ferro. MÉTODOS: Estudo de avaliação de painéis repetidos, desenvolvido em serviços públicos de saúde de municípios das cinco regiões brasileiras. Dados retrospectivos foram obtidos de 12.119 prontuários de gestantes distribuídas em dois grupos: antes da fortificação, com parto anterior a junho de 2004, e após a fortificação, com última menstruação após junho de 2005. Anemia foi definida como Hb < 11,0 g/dL. Valores de Hb/idade gestacional foram avaliados segundo dois referenciais da literatura. Foram utilizados teste qui-quadrado, t de Student e regressão logística, com nível de 5% de significância. RESULTADOS: Na amostra total, anemia caiu de 25% para 20% após fortificação (p < 0,001), com médias de Hb significativamente maiores no grupo "após" (p < 0,001). Observaram-se, entretanto, diferenças regionais importantes: reduções significativas nas regiões Nordeste (37% para 29%) e Norte (32% para 25%), onde as prevalências de anemia eram elevadas antes da fortificação, e reduções menores nas regiões Sudeste (18% para 15%) e Sul (7% para 6%), onde as prevalências eram baixas. Os níveis de Hb/idade gestacional de ambos os grupos se mostraram discretamente mais elevados nos primeiros meses, porém bem mais baixos após o terceiro ou quarto mês, dependendo da referência utilizada para comparação. Análise de regressão logística mostrou que grupo, região geográfica, situação conjugal, trimestre gestacional, estado nutricional inicial e gestação anterior associaram-se com anemia (p < 0,05). CONCLUSÕES: A prevalência de anemia diminuiu após a fortificação, porém continua elevada nas regiões Nordeste e Norte. Embora a fortificação possa ter tido papel nesse resultado favorável, há que se considerar a contribuição de outras políticas públicas implementadas no período estudado

On Developing Ridge Regression Parameters: A Graphical investigation

In this paper we have reviewed some existing and proposed some new estimators for estimating the ridge parameter "k" . All in all 19 different estimators have been studied. The investigation has been carried out using Monte Carlo simulations. A large number of different models were investigated where the variance of the random error, the number of variables included in the model, the correlations among the explanatory variables, the sample size and the unknown coefficients vectors "beta" have been varied. For each model we have performed 2000 replications and presented the results both in term of figures and tables. Based on the simulation study, we found that increasing the number of correlated variable, the variance of the random error and increasing the correlation between the independent variables have negative effect on the MSE. When the sample size increases the MSE decreases even when the correlation between the independent variables and the variance of the random error are large. In all situations, the proposed estimators have smaller MSE than the ordinary least squared and some other existing estimators.Linear Model; LSE; MSE; Monte Carlo simulations; Multicollinearity; Ridge Regression;