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106 results on '"Ferreira, Dário"'

3. Inference in mixed models with a mixture of distributions and controlled heteroscedasticity.

Author

Ferreira, Dário, Ferreira, Sandra S., Antunes, Patrícia, Oliveira, Teresa A., and Mexia, Jo∼ao T.

Abstract

Abstract.In the realm of mixed models, this article explores the estimation method for incorporating a mixture of distributions and addressing controlled heteroscedasticity. By relaxing the assumptions of normality and homoscedasticity, we introduce a more flexible approach to analyzing data. The article presents estimation techniques for variance components, estimable vectors, and cumulants, while also developing prediction intervals and prediction ellipsoids for future observations. A numerical example is employed to illustrate the method and compare it with traditional ANOVA and Bayesian estimation methods. The results demonstrate the superior flexibility and broader applicability of the proposed methods in diverse contexts. By extending the analysis beyond conventional assumptions, these approaches enhance the accuracy and robustness of statistical inference in mixed models. [ABSTRACT FROM AUTHOR]

Published
2024
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4. Measuring Sphericity in Positive Semi-Definite Matrices.

Author

Ferreira, Dário and Ferreira, Sandra S.

Subjects
*RANDOM matrices, *ASYMPTOTIC normality, *GAUSSIAN distribution, *STATISTICS, *MATRICES (Mathematics)
Abstract

The measure of sphericity for positive semi-definite matrices plays a crucial role in understanding their geometric properties, especially in high-dimensional settings. This paper introduces a robust measure of sphericity, which remains invariant under orthogonal transformations and scaling. We explore its behavior in finite-dimensional cases. Additionally, we investigate the stochastic case by considering a normal distribution, analyzing the asymptotic normality of random matrices and its implications on the convergence properties of the proposed measure. [ABSTRACT FROM AUTHOR]

Published
2024
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7. Localized holes and delocalized electrons in photoexcited inorganic perovskites: Watching each atomic actor by picosecond X-ray absorption spectroscopy

Author

Santomauro, Fabio G., Grilj, Jakob, Mewes, Lars, Nedelcu, Georgian, Yakunin, Sergii, Rossi, Thomas, Capano, Gloria, Haddad, André Al, Budarz, James, Kinschel, Dominik, Ferreira, Dario S., Rossi, Giacomo, Tovar, Mario Gutierrez, Grolimund, Daniel, Samson, Valerie, Nachtegaal, Maarten, Smolentsev, Grigory, Kovalenko, Maksym V., and Chergui, Majed

Subjects
Condensed Matter - Materials Science
Abstract

We report on an element-selective study of the fate of charge carriers in photoexcited inorganic CsPbBr3 and CsPb(ClBr)3 perovskite nanocrystals (NCs) in toluene solutions using time-resolved X-ray absorption spectroscopy with 80 ps time resolution. Probing the Br K-edge, the Pb L3-edge and the Cs L2-edge, we find that holes in the valence band are localized at Br atoms, forming small polarons, while electrons appear as delocalized in the conduction band. No signature of either electronic or structural changes are observed at the Cs L2-edge. The results at the Br and Pb edges suggest the existence of a weakly localized exciton, while the absence of signatures at the Cs edge indicates that the Cs+ cation plays no role in the charge transport, at least beyond 80 ps. These results can explain the rather modest charge carrier mobilities in these materials., Comment: 19 pages, 3 figures

Published
2016

13. Bi-additive models for extremes.

Author

Antunes, Patrícia, Ferreira, Sandra S., Ferreira, Dário, and Mexia, João T.

Subjects
CUMULANTS, ELLIPSOIDS
Abstract

To widen the application field of mixed models we introduce bi-additive models. These models are given by the sum of a fixed term X 0 β and independent random effects terms X i Z i , i = 1 , ... , w. Vectors Z 1 , ... , Z w , will have c 1 , ... , c w , i. i. d. components with r − th order cumulants χ r , 1 , ... , χ r , w. We now consider the case in which the distributions of these components are distributed as Gumbel, Fréchet and Weibull types, estimating their cumulants and parameters. We then obtain 1 − p confidence ellipsoids with [approximate] probability of containing realizations of the model. These ellipsoids can be used to, trough duality, test hypothesis on the fixed effects part X 0 β of the models. Moreover matrices X 0 , X 1 , ... , X w , contain in their columns values of controlled variables and, for given values of the controlled variables, prediction intervals are obtained, containing future observations, with 1 − p [approximate] probability. Three simulations studies, one for each distribution type, and an application to the Tagus river floods are included. We thus show how bi-additive models may be introduced in the important field of extreme value. [ABSTRACT FROM AUTHOR]

Published
2023
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17. Editorial Summary: Mathematical Models and Methods in Various Sciences.

Author

Ferreira, Dário

Subjects
*PROPORTIONAL hazards models, *QUALITY control charts, *MATHEMATICAL models, *WIENER processes, *PROPORTIONAL representation, *GARCH model
Abstract

The Special Issue of Symmetry titled "Mathematical Models and Methods in Various Sciences" brings together innovative papers on the theory, methodology, and applications of symmetric/asymmetric mathematical models and methods in various areas of science. The published papers cover a wide range of topics, including estimation methods for mismeasured covariates, empirical models for data analysis, computational approaches for heat transport, investment and pricing strategies, memory-type control charts for monitoring operations, estimation of volatility function in GARCH models, novel weighted distributions, degradation modeling, queueing systems, bivariate proportional hazard models, proportional representation in elections, bounded rational decision-making models, and reliability estimation using a Wiener process. The papers demonstrate the adaptability and capabilities of mathematical modeling in resolving complex issues across diverse scientific fields. [Extracted from the article]

Published
2023
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20. Multiple additive models

Author

Antunes, Patrícia, Ferreira, Sandra S., Ferreira, Dário, Mexia, João T., and uBibliorum

Subjects
Mixed Models, Statistics and Probability, Combinatorics, Mixed model, ANOVA, Cumulants, Additive model, Base (exponentiation), Mathematics
Abstract

The models constituting a multiple model will correspond to d treatments of a base design. Using a classic result on cumulant generation function we show how to obtain least square estimators for cumulants and generalized least squares estimators for vectors \beta, l=1,...,d, in the individual models. Next we carry out ANOVA-like analysis for the action of the factors in the base design. This is possible since the estimators \tilde{\beta }(l) of \beta (l). l=1,...,d, have, approximately, the same covariance matrix. The eigenvectors of that matrix will give the principal estimable functions \epsilon_{i}^{\top} \beta (l) i=1,...,k, l=1,...,d, for the individual models. The ANOVA-like analysis will consider homologue components on principal estimable functions. To apply our results we assume the factors in the base design to have fixed effects. Moreover if w=1, and Z(1) has covariance matrix \sigma^{2} \m I_{n}, our treatment generalizes that previously given for multiple regression designs. In them we have a linear regression for each treatment of a base design. We then study the action of the factors on that design on the vectors \beta(l), l=1,...,d. An example of application of the proposed methodology is given.

Published
2020

23. Confidence intervals and ellipsoids for estimable functions and estimable vectors in models with orthogonal block structure.

Author

Ferreira, Sandra S., Ferreira, Dário, Nunes, Célia, and Mexia, João T.

Subjects
*CONFIDENCE intervals, *VECTOR valued functions, *ORTHOGONAL functions, *CONFIDENCE regions (Mathematics), *PARAMETERS (Statistics), *SPACE-time block codes
Abstract

Sub‐models of mixed linear models are considered. The independence of these sub‐models leads to sufficient statistics for the parameters relevant for their densities. Using pivot variables, confidence regions are obtained as well hypothesis testing for variance components, estimable functions, and estimable vectors. In addition, to compare the estimators and the models, we present the histograms with the empirical joint densities for positive and negative parts of the estimators. The figures, for the two‐dimensional charts, contain the corresponding UMVUE and are all unimodal with the UMVUE near the mode. The nearness of the estimators and the modes validates the presented methodology and allows the safe use of induced densities. A numerical example applied to real data is presented. [ABSTRACT FROM AUTHOR]

Published
2023
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24. Caracterização das tentativas de suicídio no Serviço de Urgência do Hospital Sousa Martins, Unidade Local de Saúde da Guarda, EPE

Author

Santos, Mário J., Nunes, Juliana, Ferreira, Dário, and Pissarra da Costa, António

Subjects
Psychiatry, Suicide, RC435-571, Psychology, Emergency Department, Suicídio, Attempted suicide, Tentativa de suicídio, humanities, Serviço de Urgência, BF1-990
Abstract

Introduction: Suicide is a complex public health problem resulting from the interaction between biological, psychological and sociocultural factors. Annually, according to the World Health Organization, about one million individuals commit suicide worldwide. That number corresponds to half of all violent deaths recorded and the tendency is to increase. Attempted suicide is defined as an act carried out by an individual who seeks his own death, but for various reasons, usually unrelated to the individual, results frustrated. The most important predictive factor of suicide is attempted suicide. It is considered that for every person who commits suicide, 20 or more make an attempt. Aims: To analyze the profile of the patient who resorts to the Emergency Department of Sousa Martins Hospital, ULS Guarda, E.P.E., for attempted suicide. Methods: Study, of retrospective basis, of the period between 1 January 2010 and 31 December 2014. We based it on the statistical survey of data from medical records of the individuals over 18 who resorted to the Emergency Department of Sousa Martins Hospital, ULS Guarda, E.P.E., for whom it was deemed an attempted suicide event, prior to clinical evaluation. Results and Conclusions: We conclude that the typical profile of the person who resorts, for suicide attempt, to the studied Emergency Department is female, at the beginning of middle age (approximately, at age 45), married, have a history of depressive disorder, use as a method of attempt drug ingestion and point out the existence of relational problems as a triggering factor. In addition, these individuals tend to resort to the Emergency Department, especially, in the last eight hours of the day., Introdução: O suicídio é um complexo problema de saúde pública, resultante da interação entre fatores biológicos, psicológicos e socioculturais. Suicidam-se anualmente, em todo o mundo, segundo a Organização Mundial de Saúde, cerca de um milhão de indivíduos, o que corresponde a metade de todas as mortes violentas registadas, tendo esse número tendência a aumentar. A tentativa de suicídio é definida como um ato levado a cabo por um indivíduo que visa a sua morte, mas que, por razões diversas, geralmente alheias ao indivíduo, resulta frustrado. O fator de predição mais importante do suicídio é a tentativa de suicídio. Considera-se que, por cada pessoa que se suicida, 20 ou mais cometem uma tentativa de suicídio. Objetivos: Analisar o perfil do doente que recorre ao Serviço de Urgência do Hospital Sousa Martins, ULS da Guarda, E.P.E., por tentativa de suicídio. Métodos: Estudo, de carácter retrospetivo, do período compreendido entre 1 de janeiro de 2010 e 31 de dezembro de 2014. Executámos o levantamento estatístico e análise dos dados dos processos clínicos dos indivíduos maiores de 18 anos que recorreram ao Serviço de Urgência do Hospital Sousa Martins, ULS da Guarda, E.P.E., para os quais foi presumido, antes da avaliação clínica, um evento de tentativa de suicídio. Resultados e Conclusões: Concluímos que o perfil típico do indivíduo que recorre por tentativa de suicídio, ao Serviço de Urgência estudado, é ser do sexo feminino, estar no início da meia-idade (por volta dos 45 anos), ser casado/a, ter antecedentes de perturbação depressiva, utilizar como método da tentativa a ingestão medicamentosa e apontar como motivo desencadeante a existência de problemas relacionais. Além disto, estes indivíduos tendem a recorrer ao Serviço de Urgência, principalmente, nas últimas oito horas do dia.

Published
2021

25. Inference in nonorthogonal mixed models.

Author

Ferreira, Dário, Ferreira, Sandra S., Nunes, Célia, and Mexia, João T.

Subjects
*CONFIDENCE regions (Mathematics), *LEAST squares, *BAYESIAN analysis, *CONFIDENCE intervals, *ANALYSIS of variance
Abstract

This paper presents an estimation method for the random effect parameters and the variance components in linear mixed models. These models may be orthogonal or nonorthogonal. In particular, least squares estimators and the corresponding confidence regions, based on the estimation of quantiles, are considered. As to the random effects parameters, it is only assumed that they have null mean vectors and distributions with known dispersion parameters and second order moments. So, it is not necessary that they are normally distributed. A numerical example considering the normal and the gamma distributions is included, where a comparison with the analysis of variance and a Bayesian estimation based method is provided. [ABSTRACT FROM AUTHOR]

Published
2022
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29. Multiple additive models.

Author

Antunes, Patrícia, Ferreira, Sandra S., Ferreira, Dário, and Mexia, João T.

Subjects
LEAST squares, FACTOR analysis, CUMULANTS, EIGENVECTORS, FIXED effects model
Abstract

The models constituting a multiple model will correspond to d treatments of a base design. When we have individual additive models Y (l) = X 0 β (l) + ∑ i = 1 w X i Z i (l) , l = 1 , ... , d , with Z 1 (l) , ... , Z w (l) , independent, with c 1 , ... , c w independent components, with χ r , 1 , ... , χ r , w , the r − th order cumulants, r = 2 , 3 , 4 , the multiple model will be additive. Using a classic result on cumulant generation function we show how to obtain least square estimators for cumulants and generalized least squares estimators for vectors β , l = 1 , ... , d , in the individual models. Next we carry out ANOVA-like analysis for the action of the factors in the base design. This is possible since the estimators β ˜ (l) of β (l) l = 1 , ... , d , have, approximately, the same covariance matrix. The eigenvectors of that matrix will give the principal estimable functions ϵ i ⊤ β (l) i = 1 , ... , k , l = 1 , ... , d , for the individual models. The ANOVA-like analysis will consider homolog components on principal estimable functions. To apply our results we assume the factors in the base design to have fixed effects. Moreover if w = 1 , and Z (1) has covariance matrix σ 2 I n , our treatment generalizes that previously given for multiple regression designs. In them we have a linear regression for each treatment of a base design. We then study the action of the factors on that design on the vectors β (l) , l = 1 , ... , d. An example of application of the proposed methodology is given. [ABSTRACT FROM AUTHOR]

Published
2021
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30. Limit distributions for asymptotically linear statistics with spherical error

Author

Nunes, Célia, Ferreira, Dário, Ferreira, Sandra S., Mexia, João T., and uBibliorum

Subjects
Statistics and Probability, Asymptotically linear, Work (thermodynamics), Control and Optimization, Asymptotic linearity, Normal distribution, Spherical densities, Asymptotic linearity, Limit distributions, Normal distribution, Spherical densities, Cylinder volume, Artificial Intelligence, Homoscedasticity, Signal Processing, Statistics, Limit distributions, Cylinder, Cylinder volume, Computer Vision and Pattern Recognition, Limit (mathematics), lcsh:Probabilities. Mathematical statistics, Statistics, Probability and Uncertainty, lcsh:QA273-280, Information Systems, Mathematics
Abstract

Submitted by FERREIRA (dario@ubi.pt) on 2020-02-05T17:46:37Z No. of bitstreams: 1 2018 - Limit Distributions for Asymptotically Linear Statistics with Spherical Error.pdf: 109442 bytes, checksum: fea755ae8a80328f562c7b498bfe0926 (MD5) Approved for entry into archive by Pessoa (pfep@ubi.pt) on 2020-02-06T14:29:51Z (GMT) No. of bitstreams: 1 2018 - Limit Distributions for Asymptotically Linear Statistics with Spherical Error.pdf: 109442 bytes, checksum: fea755ae8a80328f562c7b498bfe0926 (MD5) Approved for entry into archive by Pessoa (pfep@ubi.pt) on 2020-02-06T14:36:35Z (GMT) No. of bitstreams: 1 2018 - Limit Distributions for Asymptotically Linear Statistics with Spherical Error.pdf: 109442 bytes, checksum: fea755ae8a80328f562c7b498bfe0926 (MD5) Made available in DSpace on 2020-02-06T14:36:35Z (GMT). No. of bitstreams: 1 2018 - Limit Distributions for Asymptotically Linear Statistics with Spherical Error.pdf: 109442 bytes, checksum: fea755ae8a80328f562c7b498bfe0926 (MD5) Previous issue date: 2018 info:eu-repo/semantics/publishedVersion

Published
2018

31. Estimation of variance components in models with positive commutativity orthogonal block structure

Author

Ferreira, Sandra S., Ferreira, Dário, Nunes, Célia, Mexia, João T., and uBibliorum

Subjects
Estimation, Block structure, Simple (abstract algebra), Numerical analysis, Linear model, Orthogonal block structure, Applied mathematics, Variance components, Estimator, Linear models, Commutative property, Mathematics
Abstract

Submitted by FERREIRA (dario@ubi.pt) on 2020-02-05T18:56:40Z No. of bitstreams: 1 2018 - Estimation of Variance Components in Models with Positive Commutativity Orthogonal Block Structure.pdf: 516997 bytes, checksum: e0d2abf568b9f1cc9e4ce1cda0c2365f (MD5) Rejected by Pessoa (pfep@ubi.pt), reason: Agregar os nomes ao OCID e/ou Ciência Vitae Colocar resumos e palavras chave Colocar código de financiamento FCT Consultar : https://www.ubi.pt/Ficheiros/Sites/7/Documentos/1375/Instruções%20para%20Auto%20depósito%20de%20documentos.pdf Após corrigir é só submeter de novo. Obrigado on 2020-02-06T15:57:05Z (GMT) Submitted by FERREIRA (dario@ubi.pt) on 2020-02-07T10:07:13Z No. of bitstreams: 1 2018 - Estimation of Variance Components in Models with Positive Commutativity Orthogonal Block Structure.pdf: 516997 bytes, checksum: e0d2abf568b9f1cc9e4ce1cda0c2365f (MD5) Approved for entry into archive by Pessoa (pfep@ubi.pt) on 2020-02-07T15:13:25Z (GMT) No. of bitstreams: 1 2018 - Estimation of Variance Components in Models with Positive Commutativity Orthogonal Block Structure.pdf: 516997 bytes, checksum: e0d2abf568b9f1cc9e4ce1cda0c2365f (MD5) Approved for entry into archive by Pessoa (pfep@ubi.pt) on 2020-02-07T15:14:30Z (GMT) No. of bitstreams: 1 2018 - Estimation of Variance Components in Models with Positive Commutativity Orthogonal Block Structure.pdf: 516997 bytes, checksum: e0d2abf568b9f1cc9e4ce1cda0c2365f (MD5) Made available in DSpace on 2020-02-07T15:14:30Z (GMT). No. of bitstreams: 1 2018 - Estimation of Variance Components in Models with Positive Commutativity Orthogonal Block Structure.pdf: 516997 bytes, checksum: e0d2abf568b9f1cc9e4ce1cda0c2365f (MD5) Previous issue date: 2018 info:eu-repo/semantics/publishedVersion

Published
2018

35. Considering the sample sizes as truncated Poisson random variables in mixed effects models.

Author

Nunes, Célia, Moreira, Elsa, Ferreira, Sandra S., Ferreira, Dário, and Mexia, João T.

Subjects
POISSON processes, POISSON distribution, ANALYSIS of variance, HOSPITAL patients, RANDOM variables, CANCER patients, SAMPLING (Process)
Abstract

When applying analysis of variance, the sample sizes may not be previously known, so it is more appropriate to consider them as realizations of random variables. A motivating example is the collection of observations during a fixed time span in a study comparing, for example, several pathologies of patients arriving at a hospital. This paper extends the theory of analysis of variance to those situations considering mixed effects models. We will assume that the occurrences of observations correspond to a counting process and the sample dimensions have Poisson distribution. The proposed approach is applied to a study of cancer patients. [ABSTRACT FROM AUTHOR]

Published
2020
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36. Tests and relevancies for the hypotheses of an orthogonal family in a model with orthogonal block structure.

Author

Ferreira, Dário, Ferreira, Sandra S., Nunes, Célia, and Mexia, João T.

Subjects
*ORTHOGRAPHIC projection, *COVARIANCE matrices, *HYPOTHESIS, *RELEVANCE, *RANDOM effects model
Abstract

A model has an orthogonal block structure if it has, as covariance matrix, a linear combination of pairwise orthogonal projection matrices, that add up to the identity matrix. The range space of these matrices are associated to hypotheses of an orthogonal family. In this paper we show how to obtain tests for these hypotheses when normality is assumed and how to consider their relevance when normality is discarded. Besides the notion of relevance, we formulate hypotheses in a general way that may be applied to models with orthogonal block structure, whose factors may have fixed and/or random effects. The results are applied to prime basis factorial models and an example is presented. [ABSTRACT FROM AUTHOR]

Published
2020
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40. One-way fixed effects ANOVA with missing observations

Author

Nunes, Célia, Capistrano, Gilberto, Ferreira, Dário, Ferreira, Sandra S., Mexia, João T., and uBibliorum

Subjects
Missing observations, ANOVA, Geography, Random sample sizes, Statistics, Econometrics, Cancer registries, Analysis of variance, Melanoma skin cancer
Abstract

Submitted by FERREIRA (dario@ubi.pt) on 2020-02-05T22:13:42Z No. of bitstreams: 1 2015 - One-way Fixed Effects ANOVA with Missing Observation.pdf: 117720 bytes, checksum: de2ba26831fe1a3a294cccc47175ccd1 (MD5) Approved for entry into archive by Pessoa (pfep@ubi.pt) on 2020-02-06T16:13:27Z (GMT) No. of bitstreams: 1 2015 - One-way Fixed Effects ANOVA with Missing Observation.pdf: 117720 bytes, checksum: de2ba26831fe1a3a294cccc47175ccd1 (MD5) Approved for entry into archive by Pessoa (pfep@ubi.pt) on 2020-02-06T16:15:38Z (GMT) No. of bitstreams: 1 2015 - One-way Fixed Effects ANOVA with Missing Observation.pdf: 117720 bytes, checksum: de2ba26831fe1a3a294cccc47175ccd1 (MD5) Made available in DSpace on 2020-02-06T16:15:39Z (GMT). No. of bitstreams: 1 2015 - One-way Fixed Effects ANOVA with Missing Observation.pdf: 117720 bytes, checksum: de2ba26831fe1a3a294cccc47175ccd1 (MD5) Previous issue date: 2015 info:eu-repo/semantics/publishedVersion

Published
2015

43. Estimation in mixed models through three step minimization.

Author

Ferreira, Dário, Ferreira, Sandra S., Nunes, Célia, and Mexia, João T.

Subjects
*ESTIMATION theory, *FIXED effects model, *ANALYSIS of variance, *MAXIMUM likelihood statistics, *ALGORITHMS
Abstract

The aim of this article is to present an estimation procedure for both fixed effects and variance components in linear mixed models. This procedure consists of a maximum-likelihood method which we call Three Step Minimization (TSM). The major contribution of this method is that when variances tend to be null standard algorithms behave badly, unlike the TSM method, which uses a grid search algorithm in a compact set. A numerical application with real and simulated data is provided. [ABSTRACT FROM PUBLISHER]

Published
2017
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44. Estimation of Variance Components in Normal Linear Mixed Models with Additivity.

Author

Ferreira, Dário, Ferreira, Sandra S., Nunes, Célia, and Mexia, João T.

Subjects
*ANALYSIS of variance, *LINEAR statistical models, *PARAMETER estimation, *JORDAN algebras, *MATHEMATICAL models
Abstract

In this paper we use commutative Jordan Algebras to estimate variance components in linear mixed models. We apply the theory to a model in which three factors cross and one of the factors is additive to the other two. [ABSTRACT FROM AUTHOR]

Published
2015
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45. Fixed effects ANOVA: an extension to samples with random size.

Author

Nunes, Célia, Ferreira, Dário, Ferreira, Sandra S., and Mexia, João T.

Subjects
*ANALYSIS of variance, *FIXED effects model, *STATISTICAL sampling, *SAMPLE size (Statistics), *DATABASES, *DEGREES of freedom
Abstract

In many relevant situations, such as in medical research, sample sizes may not be previously known. The aim of this paper is to extend one and more than one-way analysis of variance to those situations and show how to compute correct critical values. The interest of this approach lies in avoiding false rejections obtained when using the classical fixed sizeF-tests. Sample sizes are assumed as random and we then proceed with the application of this approach to a database on cancer. [ABSTRACT FROM AUTHOR]

Published
2014
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46. Ruturas de stock causadas pelo vírus SARSCoV-2 em Farmácias Comunitárias. Experiência Profissionalizante na Vertente de Farmácia Comunitária e Investigação

Author

Martins, Ana Margarida Marques, Oliveira, Maria Elisa Cairrão Rodrigues, and Ferreira, Dário Jorge da Conceição

Subjects
Sars-Cov-2, Desinfetantes, Dispostivos Médicos, Medicamentos, Stock, Farmácia Comunitária, Equipamentos de Proteção Individual
Abstract

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Published
2021

47. Modelos Mistos Ortogonais com Amostras de Dimensão Aleatória

Author

Mário, Anacleto César Xavier, Nunes, Célia Maria Pinto, and Ferreira, Dário Jorge da Conceição

Subjects
ANOVA, Amostras de dimensão aleatória, Ciências Naturais::Matemáticas [Domínio/Área Científica], Situações de estabilidade, Desemprego na União Europeia, Modelos mistos ortogonais
Abstract

Submitted by Pessoa (pfep@ubi.pt) on 2021-04-08T16:04:47Z No. of bitstreams: 1 7 - Tese_Modelos Mistos Ortogonais com Amostras de Dimensão Aleatória.pdf: 643461 bytes, checksum: 1da251d9122f67b5d7af3288633cf514 (MD5) Approved for entry into archive by Pessoa (pfep@ubi.pt) on 2021-04-08T16:04:59Z (GMT) No. of bitstreams: 1 7 - Tese_Modelos Mistos Ortogonais com Amostras de Dimensão Aleatória.pdf: 643461 bytes, checksum: 1da251d9122f67b5d7af3288633cf514 (MD5) Made available in DSpace on 2021-04-08T16:05:00Z (GMT). No. of bitstreams: 1 7 - Tese_Modelos Mistos Ortogonais com Amostras de Dimensão Aleatória.pdf: 643461 bytes, checksum: 1da251d9122f67b5d7af3288633cf514 (MD5) Previous issue date: 2020-11-26

Published
2020

48. Mortalidade perinatal na Região da Beira Interior: uma revisão de 20 anos

Author

Oliveira, Catarina Isabel Barrosa, Rodrigues, Nélia Lamberta Pereira, and Ferreira, Dário Jorge da Conceição

Subjects
Fatores de Risco, Ciências Médicas::Ciências da Saúde::Medicina [Domínio/Área Científica], Epidemiologia, Obstetrícia, Mortalidade Perinatal, Neonatologia
Abstract

Made available in DSpace on 2020-12-14T14:23:19Z (GMT). No. of bitstreams: 1 7541_16017.pdf: 2008683 bytes, checksum: a56d1110ae895010cb327fb941d1450c (MD5) Previous issue date: 2020-07-24

Published
2020

49. Avaliação da qualidade de vida das crianças com alergia às proteínas do leite de vaca dos 0-12 anos

Author

Videira, Ana Sofia da Silva Cavaco Garcia, Costa, Ricardo Jorge Barros da, and Ferreira, Dário Jorge Conceição

Subjects
Alergia Às Proteínas do Leite de Vaca, Ciências Médicas::Ciências da Saúde::Medicina [Domínio/Área Científica], Alergia Alimentar, Leite de Vaca, Crianças, Qualidade de Vida
Abstract

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Published
2018

50. Variance Components Estimation In Mixed Linear Models

Author

Adilson de Jesus Martins da Silva, Fonseca, Miguel, and Ferreira, Dário

Subjects
Sub-diagonalizations, Variance components, Sub-D, Engenharia e Tecnologia::Outras Engenharias e Tecnologias [Domínio/Área Científica], Mixed Linear Models
Abstract

This work aim to introduce a new method of estimating the variance components in mixed linear models. The approach will be done firstly for models with three variance components and secondly attention will be devoted to general case of models with an arbitrary number of variance components. In our approach, we construct and apply a finite sequence of orthogonal transformations, here named sub - diagonalizations, to the covariance structure of the mixed linear model producing a set of Gauss-Markov sub-models which will be used to create pooled estimators for the variance components. Indeed, in order to reduce the bias, we apply the sub - diagonalizations to its correspondent restricted model, that is its projection onto the orthogonal subspace generated by the columns of its mean design matrix. Thus, the Gauss - Markov sub-models will be centered. The produced estimator will be called Sub-D. Finally, the numerical behavior of the proposed estimator is examined for the case of models with three variance components, comparing its performance to the ones obtained with the REML and ANOVA estimators. Numerical results show that Sub-D produces reasonable and comparable estimates, some times slightly better than those obtained with REML and mostly better than those obtained with ANOVA. Due to the correlation between the sub-models, the estimated variability of the variability of Sub-D will be slightly bigger than the one of the REML estimator. In attempt to solve this problem a new estimator will be introduced.

Published
2017

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