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Rua do Curral - Margaride - 4610-156 Felgueiras
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ciicesi@estg.ipp.pt
Luís Grilo
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[{"id":"P-00Z-7SD","modifiedTime":1698680693,"title":"Modeling the facets of burnout in Lisbon airport border officers using PLSc-SEM estimator","year":"2023","authors":["Grilo, LM","Braz, TF","Grilo, HL","Maidana, JP","Stehlík, M"],"type":"Article in Press","publicationTitle":"STOCHASTIC ANALYSIS AND APPLICATIONS","abstract":"Border officers experience stressful moments during the working day at the border point at Lisbon airport (Portugal) that can lead to emotional exhaustion, which is the core component of burnout, and relates with cognitive fatigue (weariness) and physical fatigue. These theoretical concepts cannot be measured (or observed) directly by what are considered latent variables/constructs that are available in Shirom-Melamed Burnout Measure (SMBM). These constructs are, however, operationalized by the questions available in the SMBM, which correspond to observed variables (or manifest variables) expressed in an ordinal scale of seven categories. This questionnaire, reliable and internationally validated, was used in our research and considering the specialized literature, we proposed a hypothetical structural path model that expresses a priori perceptions about the causal relationships between the mentioned latent constructs, where physical fatigue is the target construct. A reflective model was estimated based on the sample of primary data and using a Variance-Covariance estimator of Structural Equations Modeling (VB-SEM), the consistent Partial Least Squares (PLSc), that corrects for bias to consistently estimate SEM's with common factors. The results obtained allow a better understanding of the profile and characteristics of Portuguese border officers who work at Lisbon airport, as well as reveal that the latent exogenous construct emotional exhaustion has a high positive direct effect on the cognitive fatigue, and through this latter (mediator construct), an indirect effect on the endogenous construct physical fatigue. In turn, cognitive fatigue has the greatest positive direct effect on physical fatigue. The biggest difference identified was between the direct effect of Emotional exhaustion on Physical fatigue, which is higher for workers with more years of service, as expected. However, the multigroup analysis (using the nonparametric Permutation test) showed that this difference was not statistically significant.","doi":"10.1080/07362994.2023.2266492","issn":"0736-2994","volume":"","reference":"Grilo, LM., Braz, TF., Grilo, HL., Maidana, JP., Stehlík, M (2023). Modeling the facets of burnout in Lisbon airport border officers using PLSc-SEM estimator. STOCHASTIC ANALYSIS AND APPLICATIONS. Vol.. ISSN 0736-2994. Doi 10.1080/07362994.2023.2266492. "},{"id":"P-00R-GKA","modifiedTime":1582311407,"title":"The use of information and communication technologies to overcome reading difficulties. statistical comparison of reading results through the use of Letrinhas software","year":"2019","authors":["Marques, CG","Manso, A","Grilo, LM","Ferreira, AP","Carvalho, AA"],"type":"Proceedings Paper","publicationTitle":"AIP Conference Proceedings","abstract":"Letrinhas is an information system created by the Polytechnic Institute of Tomar (Portugal), in partnership with a School Grouping (Portugal), to give support to elementary school children with reading difficulties. The software can be used on mobile devices, such as a tablet, and allows the evaluation and improvement of reading fluency. By promoting the development of students' reading skills, it contributes to the development of autonomous readers and consequently to the improvement of school results. In order to evaluate the importance of Letrinhas software in the process of reading (children from 2nd and 3rd grade, with a mean age of 7/8 years old), two independent samples were collected, consisting of students from several primary schools. A sample is made up of students who have learned from Letrinhas (experimental group) and the other sample consists of students who have learned to read through the classic process (control group). In the students' learning process there are two essential reading components: fluency and precision. To statistically compare the data gathered for the variables Fluency Index and Precision Index, in both groups (experimental and control), confidence intervals and (non)parametric tests were used. The differences between the two teaching methods of reading, observed in graphs and in the values of some descriptive statistical measures, are statistically significant (also the values obtained for the effect sizes measures are considerable). The positive impact of the Letrinhas software on the fluency and precision of reading, empirically identified by teachers, was statistically confirmed. © 2019 Author(s).","doi":"10.1063/1.5138003","issn":"0094-243X","reference":"Marques, CG., Manso, A., Grilo, LM., Ferreira, AP., Carvalho, AA (2019). The use of information and communication technologies to overcome reading difficulties. statistical comparison of reading results through the use of Letrinhas software. AIP Conference Proceedings. ISSN 0094-243X. Doi 10.1063/1.5138003. "},{"id":"P-00R-GKS","modifiedTime":1700140766,"title":"Evaluation of Academic Burnout in College Students. Application of SEM with PLS approach","year":"2019","authors":["Grilo, LM","Mubayi, A","Dinkel, K","Amdouni, B","Ren, J","Bhakta, M"],"type":"Proceedings Paper","publicationTitle":"PROCEEDINGS OF THE INTERNATIONAL CONFERENCE OF COMPUTATIONAL METHODS IN SCIENCES AND ENGINEERING 2019 (ICCMSE-2019)","abstract":"In several academic activities students experience a considerable stress in their daily life. Stressors may affect the mental and physical health of college students, leading some of them to the burnout syndrome. To evaluate this syndrome in students at Arizona State University (ASU), USA, a survey was conducted using a questionnaire previously developed, with ordinal variables. A theoretical Structural Equation Modeling (SEM) was proposed and the estimated model was obtained applying the Partial Least Squares (PLS) approach. Based on the PLS-SEM path coefficients, the latent construct behavioural stress has a direct effect on distress and insecurity, and an indirect effect on both quantitative demands and academic burnout. Both mediator constructs quantitative demands and distress have a direct effect on the academic burnout in students. A multi-group analysis was also conducted to compare the path coefficients of the estimated model by gender, but the differences are not statistically significant. These results allow a better understanding of burnout syndrome in ASU college students, which can severely limit their psychosocial well-being and performance.","doi":"10.1063/1.5138004","issn":"0094-243X","reference":"Grilo, LM., Mubayi, A., Dinkel, K., Amdouni, B., Ren, J., Bhakta, M (2019). Evaluation of Academic Burnout in College Students. Application of SEM with PLS approach. PROCEEDINGS OF THE INTERNATIONAL CONFERENCE OF COMPUTATIONAL METHODS IN SCIENCES AND ENGINEERING 2019 (ICCMSE-2019). ISSN 0094-243X. Doi 10.1063/1.5138004. "},{"id":"P-00R-GKB","modifiedTime":1700140797,"title":"A Statistical Contribution on the Film Tourism. A Case Study","year":"2019","authors":["Sol, H","Grilo, LM","Coelho, JP"],"type":"Proceedings Paper","publicationTitle":"PROCEEDINGS OF THE INTERNATIONAL CONFERENCE OF COMPUTATIONAL METHODS IN SCIENCES AND ENGINEERING 2019 (ICCMSE-2019)","abstract":"The evaluation of the impact that the images perceived by the spectators have in the destination choices they make as tourists is a growing research field, not only in Tourism and Marketing Management but also among the Behavioural Sciences. Based on a questionnaire previously developed on a Film Tourism sub-project, with qualitative variables in nominal and ordinal scale, a survey was conducted during a number of film screenings hosted by Tomar's (a medium-sized city in Portugal) Film Society. After the characterization of the random sample with the sociodemographic variables, the nonparametric test Pearson chi-square was applied to test the null hypothesis of independence between the variable Gender and the variables Have you ever visited a place by influence of a film? or Destination-dream by strong influence of a film. Given that the null hypothesis is not rejected, there is no statistical evidence to consider a dependence/relationship between these variables. Other finding is statistically significant Spearman correlations between some variables, such as Education level and The average number of activities of Film Tourism.","doi":"10.1063/1.5138002","issn":"0094-243X","reference":"Sol, H., Grilo, LM., Coelho, JP (2019). A Statistical Contribution on the Film Tourism. A Case Study. PROCEEDINGS OF THE INTERNATIONAL CONFERENCE OF COMPUTATIONAL METHODS IN SCIENCES AND ENGINEERING 2019 (ICCMSE-2019). ISSN 0094-243X. Doi 10.1063/1.5138002. "},{"id":"P-00P-FXE","modifiedTime":1535001154,"title":"Recent Studies on Risk Analysis and Statistical Modeling","year":"2018","authors":["Oliveira, TA","Kitsos, CP","Oliveira, A","Grilo, L"],"type":"Book","publicationTitle":"Contributions to Statistics","abstract":"","doi":"10.1007/978-3-319-76605-8","issn":"1431-1968","volume":"","reference":"Oliveira, TA., Kitsos, CP., Oliveira, A., Grilo, L (2018). Recent Studies on Risk Analysis and Statistical Modeling. Contributions to Statistics. Vol.. ISSN 1431-1968. Doi 10.1007/978-3-319-76605-8. "},{"id":"P-00Q-CE7","modifiedTime":1554018671,"title":"Nonparametric Individual Control Charts for Silica in Water","year":"2018","authors":["Grilo, LM","Santos, MA","Grilo, HL"],"type":"Book Chapter","publicationTitle":"Contributions to Statistics - Recent Studies on Risk Analysis and Statistical Modeling","abstract":"","doi":"10.1007/978-3-319-76605-8_9","issn":"1431-1968","volume":"","reference":"Grilo, LM., Santos, MA., Grilo, HL (2018). Nonparametric Individual Control Charts for Silica in Water. Contributions to Statistics - Recent Studies on Risk Analysis and Statistical Modeling. Vol.. ISSN 1431-1968. Doi 10.1007/978-3-319-76605-8_9. "},{"id":"P-00Q-0RY","modifiedTime":1562596268,"title":"Perfect Resources, Singularities and Scientific Tourism: Methodological Contributions to Valuation and Resources Institutionalization","year":"2018","authors":["Nunes, S","Sousa, V","Grilo, LM"],"type":"Proceedings Paper","publicationTitle":"INTERNATIONAL CONFERENCE OF COMPUTATIONAL METHODS IN SCIENCES AND ENGINEERING 2018 (ICCMSE-2018)","abstract":"Scientific tourism is an emerging economic activity that might contribute to the development of strategies to improve territorial competitiveness and cohesion. This study aims to identify some methodological options for the operationalization of scientific tourism guidelines, namely identifying and valuing resources as well as evaluating the community involvement in the process. Initially, a theoretical-conceptual framework was developed relating four structuring dimensions of analysis: territory, territorial competitiveness and cohesion, tourism and public policy. Four new concepts were also considered: perfect resources, territorial coherence, economic and territorial singularities. Since the classification and evaluation of resources are a key aspect in the development of the process to construct positive strategies to territorial competitiveness and cohesion, whose object is scientific tourism, methodological contributions were made to do so, namely through Contingent Valuation Method by applying a questionnaire with Willingness to Pay questions. Finally, a Portuguese case study was presented as an illustration.","doi":"10.1063/1.5079175","issn":"0094-243X","reference":"Nunes, S., Sousa, V., Grilo, LM (2018). Perfect Resources, Singularities and Scientific Tourism: Methodological Contributions to Valuation and Resources Institutionalization. INTERNATIONAL CONFERENCE OF COMPUTATIONAL METHODS IN SCIENCES AND ENGINEERING 2018 (ICCMSE-2018). ISSN 0094-243X. Doi 10.1063/1.5079175. "},{"id":"P-00Q-CE8","modifiedTime":1673112489,"title":"SEM using PLS Approach to assess Workers' Burnout State","year":"2018","authors":["Grilo, LM","Grilo, HL","Martire, E"],"type":"Proceedings Paper","publicationTitle":"INTERNATIONAL CONFERENCE OF COMPUTATIONAL METHODS IN SCIENCES AND ENGINEERING 2018 (ICCMSE-2018)","abstract":"In several areas, namely in Health, Education and Services in general, it is common to find people complaining that they are exposed to excessive and prolonged stress at their workplace. This situation might lead them to burnout state which, according to some experts, is characterized by symptoms as emotional and physical exhaustion. To assess this state in a Portuguese company workers, an adapted version of the Copenhagen Psychosocial Questionnaire (COPSOQ), with variables expressed in a Likert-type scale, was applied. Based on the specialized literature and authors' experience a Structural Equation Model was proposed. Based on the available dataset the estimated model was obtained after applying the Partial Least Squares approach and a bootstrap nonparametric procedure was used, namely to estimate the significance of the path coefficients. As main results, the latent construct of \"stress\" is seen as a mediator predictor of \"burnout\", as expected, and the latent constructs of \"justice\" and \"quantitative demands\" are both predictors of \"stress\" and indirect predictors of the latent construct of \"burnout\". The occupational health experts consider these results as an important tool to understand the burnout state of such workers.","doi":"10.1063/1.5079172","issn":"0094-243X","reference":"Grilo, LM., Grilo, HL., Martire, E (2018). SEM using PLS Approach to assess Workers' Burnout State. INTERNATIONAL CONFERENCE OF COMPUTATIONAL METHODS IN SCIENCES AND ENGINEERING 2018 (ICCMSE-2018). ISSN 0094-243X. Doi 10.1063/1.5079172. "},{"id":"P-00P-1CS","modifiedTime":1673112493,"title":"Hadamard Matrices and links to Information Theory","year":"2018","authors":["Francisco, C","Oliveira, TA","Oliveira, A","Grilo, L"],"type":"Proceedings Paper","publicationTitle":"INTERNATIONAL CONFERENCE OF NUMERICAL ANALYSIS AND APPLIED MATHEMATICS (ICNAAM 2017)","abstract":"The existence of Hadamard matrices remains one of the most challenging open questions in combinatorics. Substantial progress on their existence has resulted from advances in algebraic design theory using deep connections with linear algebra, abstract algebra. finite geometry, number theory, combinatorics and optimization. The construction and analysis of Hadamard matrices, and their use on combinatorial designs, play an important role nowadays in diverse fields such as: quantum information, communications, networking, cryptography, biometry and security. Hadamard Matrices are present in our daily life and they give rise to a class of block designs named Hadamard configurations. Different applications of it based on new technologies and codes of figures such as QR Codes are present almost everywhere. Balanced Incomplete Block Designs (BIBD) are very well known as a tool to solve emerging problems in this area. Illustrations and applications to authentication codes and secret sharing schemes will be presented.","doi":"10.1063/1.5044070","issn":"0094-243X","reference":"Francisco, C., Oliveira, TA., Oliveira, A., Grilo, L (2018). Hadamard Matrices and links to Information Theory. INTERNATIONAL CONFERENCE OF NUMERICAL ANALYSIS AND APPLIED MATHEMATICS (ICNAAM 2017). ISSN 0094-243X. Doi 10.1063/1.5044070. "},{"id":"P-00Q-0RZ","modifiedTime":1673112495,"title":"Evaluation of the Sugar Content along the Stalk Height of Sugarcane Plants for Different Growth Conditions. Statistical Analysis","year":"2018","authors":["Mateus, DMR","Pinho, HJO","Grilo, LM"],"type":"Proceedings Paper","publicationTitle":"INTERNATIONAL CONFERENCE OF COMPUTATIONAL METHODS IN SCIENCES AND ENGINEERING 2018 (ICCMSE-2018)","abstract":"The Brix degree is an indicator of sugarcane juice sugar content but it is not uniform along the plant stalk height. To evaluate the Brix on the height measurement of the stalk, three groups of sugarcane samples were compared. The groups consisted in different growth conditions under Portuguese mainland climate: (i) growth in a constructed wetland filled with clay brick fragments used to treat secondary wastewater; (ii) growth in a deactivated but irrigated constructed wetland filled with clay lightweight aggregate; (iii) growth in soil with irrigation. Some descriptive statistics were obtained for the three groups and 95% confidence intervals (also including bootstrap BCa procedure) were computed and compared. The one-way ANOVA demonstrates that different growth conditions do not affect the relative height position of the stalk average Brix representative internode. A simple linear regression was adjusted to model the relationship between the relative Brix with the relative measurement height and might be used to predict the sugarcane juice sugar content.","doi":"10.1063/1.5079168","issn":"0094-243X","reference":"Mateus, DMR., Pinho, HJO., Grilo, LM (2018). Evaluation of the Sugar Content along the Stalk Height of Sugarcane Plants for Different Growth Conditions. Statistical Analysis. INTERNATIONAL CONFERENCE OF COMPUTATIONAL METHODS IN SCIENCES AND ENGINEERING 2018 (ICCMSE-2018). ISSN 0094-243X. Doi 10.1063/1.5079168. "},{"id":"P-00Q-0RX","modifiedTime":1703082261,"title":"Preface of the \"symposium on Computational Data Analysis and Numerical Methods\"","year":"2018","authors":["Grilo, LM"],"type":"Editorial Material","publicationTitle":"AIP Conference Proceedings","abstract":"","doi":"10.1063/1.5079165","issn":"0094-243X","reference":"Grilo, LM (2018). Preface of the \"symposium on Computational Data Analysis and Numerical Methods\". AIP Conference Proceedings. ISSN 0094-243X. Doi 10.1063/1.5079165. "},{"id":"P-00M-HX9","modifiedTime":1544522151,"title":"The exact and near-exact distributions for the statistic used to test the reality of covariance matrix in a complex normal distribution","year":"2017","authors":["Grilo, LM","Coelho, CA"],"type":"Proceedings Paper","publicationTitle":"Springer Proceedings in Mathematics and Statistics","abstract":"The authors start by approximating the exact distribution of the negative logarithm of the likelihood ratio statistic, used to test the reality of the covariance matrix in a certain complex multivariate normal distribution, by an infinite mixture of Generalized Near-Integer Gamma (GNIG) distributions. Based on this representation they develop a family of near-exact distributions for the likelihood ratio statistic, which are finite mixtures of GNIG distributions and match, by construction, some of the first exact moments. Using a proximity measure based on characteristic functions the authors illustrate the excellent properties of the near-exact distributions. They are very close to the exact distribution but far more manageable and have very good asymptotic properties both for increasing sample sizes as well as for increasing number of variables. These near-exact distributions are much more accurate than the asymptotic approximation considered, namely when the sample size is small and the number of variables involved is large. Furthermore, the corresponding cumulative distribution functions allow for an easy computation of very accurate near-exact quantiles. © Springer International Publishing AG 2017.","doi":"10.1007/978-3-319-49984-0_20","issn":"2194-1009","reference":"Grilo, LM., Coelho, CA (2017). The exact and near-exact distributions for the statistic used to test the reality of covariance matrix in a complex normal distribution. Springer Proceedings in Mathematics and Statistics. ISSN 2194-1009. Doi 10.1007/978-3-319-49984-0_20. "},{"id":"P-00N-BRJ","modifiedTime":1673112492,"title":"Multinomial Logistic Regression in Workers' Health","year":"2017","authors":["Grilo, LM","Grilo, HL","Goncalves, SP","Junca, A"],"type":"Proceedings Paper","publicationTitle":"PROCEEDINGS OF THE INTERNATIONAL CONFERENCE OF COMPUTATIONAL METHODS IN SCIENCES AND ENGINEERING 2017 (ICCMSE-2017)","abstract":"In European countries, namely in Portugal, it is common to hear some people mentioning that they are exposed to excessive and continuous psychosocial stressors at work. This is increasing in diverse activity sectors, such as, the Services sector. A representative sample was collected from a Portuguese Services' organization, by applying a survey (internationally validated), which variables were measured in five ordered categories in Likert-type scale. A multinomial logistic regression model is used to estimate the probability of each category of the dependent variable general health perception where, among other independent variables, burnout appear as statistically significant.","doi":"10.1063/1.5012392","issn":"0094-243X","reference":"Grilo, LM., Grilo, HL., Goncalves, SP., Junca, A (2017). Multinomial Logistic Regression in Workers' Health. PROCEEDINGS OF THE INTERNATIONAL CONFERENCE OF COMPUTATIONAL METHODS IN SCIENCES AND ENGINEERING 2017 (ICCMSE-2017). ISSN 0094-243X. Doi 10.1063/1.5012392. "},{"id":"P-00N-8ZS","modifiedTime":1512578248,"title":"Axisymmetric motion of a proposed generalized non-Newtonian fluid model with shear-dependent viscoelastic effects","year":"2017","authors":["Carapau, F","Correia, P","Grilo, LM","Conceição, R"],"type":"Article","publicationTitle":"IAENG International Journal of Applied Mathematics","abstract":"Three-dimensional numerical simulations of non- Newtonian fluid flows are a challenging problem due to the particularities of the involved differential equations leading to a high computational effort in obtaining numerical solutions, which in many relevant situations becomes infeasible. Several models has been developed along the years to simulate the behavior of non-Newtonian fluids together with many different numerical methods. In this work we use a one-dimensional hierarchical approach to a proposed generalized third-grade fluid with shear-dependent viscoelastic effects model. This approach is based on the Cosserat theory related to fluid dynamics and we consider the particular case of flow through a straight and rigid tube with constant circular cross-section. With this approach, we manage to obtain results for the wall shear stress and mean pressure gradient of a real three-dimensional flow by reducing the exact three-dimensional system to an ordinary differential equation. This one-dimensional system is obtained by integrating the linear momentum equation over the constant cross-section of the tube, taking a velocity field approximation provided by the Cosserat theory. From this reduced system, we obtain the unsteady equations for the wall shear stress and mean pressure gradient depending on the volume flow rate, Womersley number, viscoelastic coefficients and the flow index over a finite section of the tube geometry. Attention is focused on some numerical simulations for constant and non-constant mean pressure gradient using a Runge-Kutta method.","doi":"","issn":"1992-9978","reference":"Carapau, F., Correia, P., Grilo, LM., Conceição, R (2017). Axisymmetric motion of a proposed generalized non-Newtonian fluid model with shear-dependent viscoelastic effects. IAENG International Journal of Applied Mathematics. ISSN 1992-9978. Doi . "},{"id":"P-00P-YT6","modifiedTime":1703082261,"title":"Financial and risk modelling with semicontinuous covariances","year":"2017","authors":["Stehlík M.","Helperstorfer C.","Hermann P.","Šupina J.","Grilo L.M.","Maidana J.P.","Fuders F.","Stehlíková S."],"type":"Article","publicationTitle":"Information Sciences","abstract":"We are encountering deep financial crisis. One of the basic problems we face is how to predict financial developments. Current modelling is clearly insufficient since continuity of autocorrelation oversmoothes the empirical financial data. We prove that geometric probability to chose positive definite continuous covariance by financial data is zero. We also have the empirical evidence for this fact from real stock data. In order to overcome this gap we introduce the novel abc class of semicontinuous covariance functions, which integrates both continuous and discontinuous covariances. The abc class of covariances is much more flexible, powerful, and realistic than its continuous counterpart. It gives answer to the question why financial markets face negative interest rates, cyclic downbreaks, and other difficulties nowadays. As it is clearly illustrated in this paper, the experimenter (e.g. the financial institution) can choose only up to some extent whether abc class member will be positive definite everywhere. To the best knowledge of the authors this fits well to the own Kolmogorov's opinions on axiomatic theory of probability. The Kolmogorov's axiomatic theory of probability was developed as one possible alternative in order to utilize the flexibility of Lebesgue integral in probability theory, but in many experiments e.g. in physics and finance, one should go beyond this axiomatics. That means one should accept negative probabilities (and consequently negative definite covariance functions). In this paper we clarify that the modeler's choice of positive/negative definite functions should be considered within broader Information Theory setup. The introduced abc class is purely topologically defined, with soft regularity conditions on covariances, which are still applicable for increasing and infill domain asymptotics for regression problems, kriging, and finance. These conditions are related to semicontinuous maps of Ornstein Uhlenbeck (OU) processes. We provide several novel results for optimal design of random fields with abc covariances, random walks in finance, and probabilities of ruins related to shocks (e.g. by earthquakes). In particular, we construct a random walk model with semicontinuous covariance. The novel abc class provides a proper environment for unifying several contradictions on IS/ML model in the economic literature. All mentioned novel economical applications are hardly visible from currently used “continuous covariance” framework.","doi":"10.1016/j.ins.2017.02.002","issn":"00200255","reference":"Stehlík M.., Helperstorfer C.., Hermann P.., Šupina J.., Grilo L.M.., Maidana J.P.., Fuders F.., Stehlíková S. (2017). Financial and risk modelling with semicontinuous covariances. Information Sciences. ISSN 00200255. Doi 10.1016/j.ins.2017.02.002. "},{"id":"P-00N-BRM","modifiedTime":1703082261,"title":"Preface of the \"symposium on Computational Data Analysis and Numerical Methods\"","year":"2017","authors":["Grilo, LM"],"type":"Editorial Material","publicationTitle":"AIP Conference Proceedings","abstract":"","doi":"10.1063/1.5012383","issn":"0094-243X","reference":"Grilo, LM (2017). Preface of the \"symposium on Computational Data Analysis and Numerical Methods\". AIP Conference Proceedings. ISSN 0094-243X. Doi 10.1063/1.5012383. "},{"id":"P-00M-3PN","modifiedTime":1673112483,"title":"Robust Statistical Approaches to Assess the Degree of Agreement of Clinical Data","year":"2016","authors":["Grilo, LM","Grilo, HL"],"type":"Proceedings Paper","publicationTitle":"PROCEEDINGS OF THE INTERNATIONAL CONFERENCE ON NUMERICAL ANALYSIS AND APPLIED MATHEMATICS 2015 (ICNAAM-2015)","abstract":"To analyze the blood of patients who took vitamin B12 for a period of time, two different medicine measurement methods were used (one is the established method, with more human intervention, and the other method uses essentially machines). Given the non-normality of the differences between both measurement methods, the limits of agreement are estimated using also a non-parametric approach to assess the degree of agreement of the clinical data. The bootstrap resampling method is applied in order to obtain robust confidence intervals for mean and median of differences. The approaches used are easy to apply, running a friendly software, and their outputs are also easy to interpret. In this case study the results obtained with (non)parametric approaches lead us to different statistical conclusions, but the decision whether agreement is acceptable or not is always a clinical judgment.","doi":"10.1063/1.4952235","issn":"0094-243X","reference":"Grilo, LM., Grilo, HL (2016). Robust Statistical Approaches to Assess the Degree of Agreement of Clinical Data. PROCEEDINGS OF THE INTERNATIONAL CONFERENCE ON NUMERICAL ANALYSIS AND APPLIED MATHEMATICS 2015 (ICNAAM-2015). ISSN 0094-243X. Doi 10.1063/1.4952235. "},{"id":"P-00M-9WY","modifiedTime":1673112485,"title":"Specific Shear-dependent Viscoelastic Third-grade Fluid Model","year":"2016","authors":["Carapau, F","Correia, P","Grilo, LM"],"type":"Proceedings Paper","publicationTitle":"Proceedings of the International Conference of Computational Methods in Sciences and Engineering 2016 (ICCMSE-2016)","abstract":"A specific modified constitutive equation for a third-grade fluid is proposed so that the model be suitable for applications where shear-thinning or shear-thickening may occur. For that, we use the Cosserat theory approach reducing the exact three-dimensional equations to a system depending only on time and on a single spatial variable. This one-dimensional system is obtained by integrating the linear momentum equation over the cross-section of the tube, taking a velocity field approximation provided by the Cosserat theory. From this reduced system, we obtain the unsteady equations for the wall shear stress and mean pressure gradient depending on the volume flow rate, Womersley number, viscoelastic coefficient and flow index over a finite section of the tube geometry with constant circular cross-section.","doi":"10.1063/1.4968737","issn":"0094-243X","reference":"Carapau, F., Correia, P., Grilo, LM (2016). Specific Shear-dependent Viscoelastic Third-grade Fluid Model. Proceedings of the International Conference of Computational Methods in Sciences and Engineering 2016 (ICCMSE-2016). ISSN 0094-243X. Doi 10.1063/1.4968737. "},{"id":"P-00M-9X3","modifiedTime":1673112486,"title":"Minisymposium on Computational Data Analysis and Numerical Methods","year":"2016","authors":["Grilo, LM"],"type":"Proceedings Paper","publicationTitle":"Proceedings of the International Conference of Computational Methods in Sciences and Engineering 2016 (ICCMSE-2016)","abstract":"","doi":"10.1063/1.4968730","issn":"0094-243X","reference":"Grilo, LM (2016). Minisymposium on Computational Data Analysis and Numerical Methods. Proceedings of the International Conference of Computational Methods in Sciences and Engineering 2016 (ICCMSE-2016). ISSN 0094-243X. Doi 10.1063/1.4968730. "},{"id":"P-00M-9X4","modifiedTime":1673112487,"title":"Individual Control Charts in Paperboard Industry","year":"2016","authors":["Grilo, LM","Silva, DS","Nogueira, IM","Grilo, HL","Oliveira, TA"],"type":"Proceedings Paper","publicationTitle":"Proceedings of the International Conference of Computational Methods in Sciences and Engineering 2016 (ICCMSE-2016)","abstract":"The stiffness of paperboard is an important continuous variable measured in the labs of paperboard industry to evaluate the quality of the final product. The variable is approximately normal distributed, in this case study, and individual control charts to monitor the stiffness are obtained based on average moving range. Since the available sample size is small we decide to estimate robust control limits using a non-parametric method based on empirical quantiles (that performs also well under the normality of the observations), with the bootstrap procedure. The comparison of the control limits should be made based on the required accuracy. We also compare the output of the stable process (i.e., in statistical control) with the process specifications and we conclude that it is not a capable process.","doi":"10.1063/1.4968738","issn":"0094-243X","reference":"Grilo, LM., Silva, DS., Nogueira, IM., Grilo, HL., Oliveira, TA (2016). Individual Control Charts in Paperboard Industry. Proceedings of the International Conference of Computational Methods in Sciences and Engineering 2016 (ICCMSE-2016). ISSN 0094-243X. Doi 10.1063/1.4968738. "},{"id":"P-00G-BCF","modifiedTime":1450299495,"title":"Individual and Moving Range Control Charts in the Production of Olive Oil","year":"2015","authors":["Grilo, LM","Grilo, HL"],"type":"Proceedings Paper","publicationTitle":"PROCEEDINGS OF THE INTERNATIONAL CONFERENCE OF NUMERICAL ANALYSIS AND APPLIED MATHEMATICS 2014 (ICNAAM-2014)","abstract":"Quality control charts are usually used to monitor peroxideindex of olive oil, which is a variableanalysedin order toassess the quality and tocharacterize the typeof oil. However, the empirical distribution of peroxideindex does not often verify the assumption of normality. In this case study, we obtained the individual and moving range charts for peroxideindex of virgin olive oil, computing the control limits using theaverage and also the median moving range. Afterwards, we compared these charts with the more efficient and robust ones, based on an adequate Box-Cox transformation. The conclusions obtained with these approaches are relatively different.","doi":"10.1063/1.4913051","issn":"0094-243X","reference":"Grilo, LM., Grilo, HL (2015). Individual and Moving Range Control Charts in the Production of Olive Oil. PROCEEDINGS OF THE INTERNATIONAL CONFERENCE OF NUMERICAL ANALYSIS AND APPLIED MATHEMATICS 2014 (ICNAAM-2014). ISSN 0094-243X. Doi 10.1063/1.4913051. "},{"id":"P-00G-EHJ","modifiedTime":1447799563,"title":"Statistical analysis of psychomotor therapy in children with attention-deficit/hyperactivity disorder","year":"2015","authors":["Grilo, L","Henriques, R","Correia, P","Grilo, H"],"type":"Article","publicationTitle":"WSEAS Transactions on Biology and Biomedicine","abstract":"One of the most common behavioural disorders in school age children, which has registered a high increase of the prevalence rate in the last decade, is Attention-deficit/hyperactivity disorder – a neurological condition that involves problems with inattention and hyperactivity-impulsivity which are developmentally inconsistent with the children’s age. It has much comorbidity affecting a child’s life in every domain with a negative influence in the prognosis of her condition. Psychomotor deficits are responsible for many of the learning disabilities of these children. A sample of children with the diagnosis of Attention-deficit/hyperactivity disorder, under psychomotor therapy followed in the Department of Child Psychiatry of Centro Hospitalar Cova da Beira (in Portugal), was submitted to a Psychomotor Battery. Nonparametric approaches (as graphical techniques and hypothesis tests) were applied to the data, collected at baseline and at the end of the intervention. The main result shows that there is a statistical significant improvement of the psychomotor profile after psychomotor therapy (supported by both total scores of Psychomotor Battery and some particular psychomotor factors).","doi":"","issn":"1109-9518","reference":"Grilo, L., Henriques, R., Correia, P., Grilo, H (2015). Statistical analysis of psychomotor therapy in children with attention-deficit/hyperactivity disorder. WSEAS Transactions on Biology and Biomedicine. ISSN 1109-9518. Doi . "},{"id":"P-00G-VNQ","modifiedTime":1450313511,"title":"Industrial production of gypsum: Quality control charts","year":"2015","authors":["Grilo, LM","Grilo, HL","Marques, CJ"],"type":"Proceedings Paper","publicationTitle":"Springer Proceedings in Mathematics and Statistics","abstract":"The production of gypsum (marketed if it accomplishes the required specifications) occurs during the process of flue gas desulphurization in a Portuguese Coal Thermoelectric Central. Important variables in this process are statistically analyzed in the chemical laboratory and quality control charts are implemented to monitor the entire process. In this study individuals and moving range charts of the variable “density of gypsum slurry” are compared with the “more efficient” ones obtained after a Box-Cox transformation. This transformation is used to normalize the data, because its observations come from non-normal models—where classical control charts are considered less appropriate, since they usually exhibit rates of false alarms different from what would be expected. Although it is important to consider different statistical approaches for quality control charts, during the monitoring of an industrial process, in this case study the achieved results lead us, essentially, to similar conclusions. © Springer International Publishing Switzerland 2015.","doi":"10.1007/978-3-319-18029-8_17","issn":"2194-1009","reference":"Grilo, LM., Grilo, HL., Marques, CJ (2015). Industrial production of gypsum: Quality control charts. Springer Proceedings in Mathematics and Statistics. ISSN 2194-1009. Doi 10.1007/978-3-319-18029-8_17. "},{"id":"P-00G-BCG","modifiedTime":1673112482,"title":"Attention-deficit/hyperactivity Disorder in Children. A Statistical Approach","year":"2015","authors":["Grilo, LM","Henriques, RS","Correia, PC","Grilo, HL"],"type":"Proceedings Paper","publicationTitle":"PROCEEDINGS OF THE INTERNATIONAL CONFERENCE OF NUMERICAL ANALYSIS AND APPLIED MATHEMATICS 2014 (ICNAAM-2014)","abstract":"Attention-deficit/hyperactivity disorder (ADHD) is one of the most common behavioural disorders in school age children, with a high increase of its prevalence rate in the last decade. ADHD has much comorbidity affecting the child's life in every domain of their quotidian life with a negative influence in the prognosis of this condition. Psychomotor deficits are responsible for many of the learning disabilities of these children. A sample was submitted to a Psychomotor Battery, in order to characterize the population of children with the diagnosis of ADHD, followed at the Centro Hospitalar Cova da Beira (Portugal), under psychomotor therapy. To the data, collected at baseline and at the end of the intervention, we applied a nonparametric testand graphical techniquesbased on limits of (dis) agreement. The main result shows that the psychomotor profile has a statistical significant improvement after psychomotor therapy.","doi":"10.1063/1.4913047","issn":"0094-243X","reference":"Grilo, LM., Henriques, RS., Correia, PC., Grilo, HL (2015). Attention-deficit/hyperactivity Disorder in Children. A Statistical Approach. PROCEEDINGS OF THE INTERNATIONAL CONFERENCE OF NUMERICAL ANALYSIS AND APPLIED MATHEMATICS 2014 (ICNAAM-2014). ISSN 0094-243X. Doi 10.1063/1.4913047. "},{"id":"P-00A-2CM","modifiedTime":1450299449,"title":"Robust Control Charts in Industrial Production of Olive Oil","year":"2014","authors":["Grilo, LM","Mateus, DMR","Alves, AC","Grilo, HL"],"type":"Proceedings Paper","publicationTitle":"INTERNATIONAL CONFERENCE OF COMPUTATIONAL METHODS IN SCIENCES AND ENGINEERING 2014 (ICCMSE 2014)","abstract":"Acidity is one of the most important variables in the quality analysis and characterization of olive oil. During the industrial production we use individuals and moving range charts to monitor this variable, which is not always normal distributed. After a brief exploratory data analysis, where we use the bootstrap method, we construct control charts, before and after a Box-Cox transformation, and compare their robustness and performance.","doi":"10.1063/1.4897794","issn":"0094-243X","reference":"Grilo, LM., Mateus, DMR., Alves, AC., Grilo, HL (2014). Robust Control Charts in Industrial Production of Olive Oil. INTERNATIONAL CONFERENCE OF COMPUTATIONAL METHODS IN SCIENCES AND ENGINEERING 2014 (ICCMSE 2014). ISSN 0094-243X. Doi 10.1063/1.4897794. "},{"id":"P-008-GR5","modifiedTime":1450245369,"title":"Near-exact Distributions for the Likelihood Ratio Statistic used to Test the Reality of a Covariance Matrix","year":"2013","authors":["Grilo, LM","Coelho, CA"],"type":"Proceedings Paper","publicationTitle":"11TH INTERNATIONAL CONFERENCE OF NUMERICAL ANALYSIS AND APPLIED MATHEMATICS 2013, PTS 1 AND 2 (ICNAAM 2013)","abstract":"In a first stage the authors show how the exact distribution of the likelihood ratio statistic used to test the reality of a covariance matrix may be expressed as the distribution of the sum of two independent random variables, one with a Generalized Integer Gamma distribution and the other with the distribution of a sum of independent Logbeta random variables. From this form of the exact distribution the authors develop then a family of near-exact distributions, based on finite mixtures of Generalized Near-Integer Gamma distributions. These near-exact distributions match, by construction, some of the first exact moments and they have very manageable cumulative distribution functions, which allow for an easy computation of sharp near-exact quantiles and p-values.","doi":"10.1063/1.4825615","issn":"0094-243X","reference":"Grilo, LM., Coelho, CA (2013). Near-exact Distributions for the Likelihood Ratio Statistic used to Test the Reality of a Covariance Matrix. 11TH INTERNATIONAL CONFERENCE OF NUMERICAL ANALYSIS AND APPLIED MATHEMATICS 2013, PTS 1 AND 2 (ICNAAM 2013). ISSN 0094-243X. Doi 10.1063/1.4825615. "},{"id":"P-002-G9C","modifiedTime":1450247449,"title":"A Family of Near-Exact Distributions Based on Truncations of the Exact Distribution for the Generalized Wilks Lambda Statistic","year":"2012","authors":["Grilo, LM","Coelho, CA"],"type":"Article","publicationTitle":"COMMUNICATIONS IN STATISTICS-THEORY AND METHODS","abstract":"For the case where at least two sets have an odd number of variables we do not have the exact distribution of the generalized Wilks Lambda statistic in a manageable form, adequate for manipulation. In this article, we develop a family of very accurate near-exact distributions for this statistic for the case where two or three sets have an odd number of variables. We first express the exact characteristic function of the logarithm of the statistic in the form of the characteristic function of an infinite mixture of Generalized Integer Gamma distributions. Then, based on truncations of this exact characteristic function, we obtain a family of near-exact distributions, which, by construction, match the first two exact moments. These near-exact distributions display an asymptotic behaviour for increasing number of variables involved. The corresponding cumulative distribution functions are obtained in a concise and manageable form, relatively easy to implement computationally, allowing for the computation of virtually exact quantiles. We undertake a comparative study for small sample sizes, using two proximity measures based on the Berry-Esseen bounds, to assess the performance of the near-exact distributions for different numbers of sets of variables and different numbers of variables in each set.","doi":"10.1080/03610926.2011.604146","issn":"0361-0926","reference":"Grilo, LM., Coelho, CA (2012). A Family of Near-Exact Distributions Based on Truncations of the Exact Distribution for the Generalized Wilks Lambda Statistic. COMMUNICATIONS IN STATISTICS-THEORY AND METHODS. ISSN 0361-0926. Doi 10.1080/03610926.2011.604146. "},{"id":"P-007-YPR","modifiedTime":1544626600,"title":"The exact and near-exact distributions for the wilks lambda statistic used in the test of independence of two sets of variables","year":"2010","authors":["Grilo, LM","Coelho, CA"],"type":"Proceedings Paper","publicationTitle":"American Journal of Mathematical and Management Sciences","abstract":"We develop the exact distribution of the Wilks Lambda statistic to test the independence of two sets of variables, both with an odd number of variables, under the form of an infinite mixture of Generalized Integer Gamma distributions. Based on truncations of the exact characteristic function, for the product of independent Beta random variables, we obtain near-exact distributions for such product and then by direct application of these results, and once again based on truncations, we develop near-exact distributions for the Wilks Lambda statistic. These near-exact distributions are finite mixtures of Generalized Integer Gamma and Generalized Near-Integer Gamma distributions. By construction, the two first moments of these approximations are equal to the exact moments. These distributions are manageable and relatively easy to implement computationally, allowing for the computation of near-exact quantiles which may indeed be regarded as virtually exact, given the good convergence properties of the series involved, mainly when the difference between the sample size and the overall number of variables involved is rather small. We assess the proximity between these near-exact distributions and the exact distribution by using two measures based on the Berry-Esseen bounds. Copyright © 2010 by Americin Sciences Press, Inc.","doi":"10.1080/01966324.2010.10737781","issn":"0196-6324","reference":"Grilo, LM., Coelho, CA (2010). The exact and near-exact distributions for the wilks lambda statistic used in the test of independence of two sets of variables. American Journal of Mathematical and Management Sciences. ISSN 0196-6324. Doi 10.1080/01966324.2010.10737781. "},{"id":"P-004-AD5","modifiedTime":1450223926,"title":"Development and comparative study of two near-exact approximations to the distribution of the product of an odd number of independent Beta random variables","year":"2007","authors":["Grilo, LM","Coelho, CA"],"type":"Article","publicationTitle":"JOURNAL OF STATISTICAL PLANNING AND INFERENCE","abstract":"Using the concept of near-exact approximation to a distribution we developed two different near-exact approximations to the distribution of the product of an odd number of particular independent Beta random variables (r.v.'s). One of them is a particular generalized near-integer Gamma (GNIG) distribution and the other is a mixture of two GNIG distributions. These near-exact distributions are mostly adequate to be used as a basis for approximations of distributions of several statistics used in multivariate analysis. By factoring the characteristic function (c.f.) of the logarithm of the product of the Beta r.v.'s, and then replacing a suitably chosen factor of that c.f. by an adequate asymptotic result it is possible to obtain what we call a near-exact c.f., which gives rise to the near-exact approximation to the exact distribution. Depending on the asymptotic result used to replace the chosen pails of the c.f., one may obtain different near-exact approximations. Moments from the two near-exact approximations developed are compared with the exact ones. The two approximations are also compared with each other, namely in terms of moments and quantiles.","doi":"10.1016/j.jspi.2006.09.005","issn":"0378-3758","reference":"Grilo, LM., Coelho, CA (2007). Development and comparative study of two near-exact approximations to the distribution of the product of an odd number of independent Beta random variables. JOURNAL OF STATISTICAL PLANNING AND INFERENCE. ISSN 0378-3758. Doi 10.1016/j.jspi.2006.09.005. "},{"id":"P-008-JGD","modifiedTime":1450300491,"title":"A mixture of Generalized Integer Gamma distributions as the exact distribution of the product of an odd number of independent Beta random variables: Applications","year":"2006","authors":["Coelho, CA","Alberto, RP","Grilo, LM"],"type":"Article","publicationTitle":"Journal of Interdisciplinary Mathematics","abstract":"In this paper we show first how the distribution of the logarithm of a random variable with a Beta distribution may be expressed either as a mixture of Gamma distributions or as a mixture of Generalized Integer Gamma (GIG) distributions and then how the exact distribution of the product of an odd number of independent Beta random variables whose first parameter evolves by 1/2 and whose second parameter is the half of an odd integer may be expressed as a mixture of GIG distributions. Some particularities of these mixtures are analysed. The results are then used to obtain the exact distribution of the logarithm of the Wilks Λ statistic to test the independence of two sets of variables, both with an odd number of variables, and the exact distribution of the logarithm of the generalized Wilks Λ statistic to test the independence of several sets of variables, in the case where two or three of them have an odd number of variables. A discussion of relative advantages and disadvantages of the use of the exact versus near-exact distributions is carried out. © Taru Publications.","doi":"10.1080/09720502.2006.10700441","issn":"0972-0502","reference":"Coelho, CA., Alberto, RP., Grilo, LM (2006). A mixture of Generalized Integer Gamma distributions as the exact distribution of the product of an odd number of independent Beta random variables: Applications. Journal of Interdisciplinary Mathematics. ISSN 0972-0502. Doi 10.1080/09720502.2006.10700441. "}]