DSpace Collection:

Twenty-five analogies for explaining statistical concepts

Tue, 09 Apr 2013 09:54:11 GMT

Title: Twenty-five analogies for explaining statistical concepts Authors: Behar, Roberto; Grima Cintas, Pedro; Marco Almagro, Lluís Abstract: The use of analogies is a resource that can be used for transmitting concepts and making classes more enjoyable. This article presents 25 analogies that we use in our introductory statistical courses for introducing concepts and clarifying possible doubts. We have found that these analogies draw students’ attention and reinforce the ideas that we want to transmit.

Linear-Angle correlation plots: New graphs for revealing correlation structure

Thu, 04 Apr 2013 07:23:09 GMT

Title: Linear-Angle correlation plots: New graphs for revealing correlation structure Authors: Graffelman, Jan Abstract: In multivariate graphics, correlations between variables are often approximated by the cosines of the angles between vectors. In practice, it is difficult to reliably estimate correlations from such displays by eye. In this article, we therefore develop new graphs, called linear-angle correlation plots, that have a linear relationship between correlation and angle, and from which correlation coefficients are read off more easily. Several multivariate datasets are used to illustrate the proposed graphs. The goodness-of-fit properties of the new graphs are compared with standard multivariate methods such as principal component analysis and principal factor analysis. Cosine-based plots typically gave the poorest approximation to the correlation matrix. A linear interpretation rule for the angle often improved the fit. The best fit was generally obtained by principal factor analysis using scalar products to approximate correlations

Experiences of simulation use in industrial projects

Fri, 22 Mar 2013 10:34:19 GMT

Title: Experiences of simulation use in industrial projects Authors: Fonseca Casas, Pau; Casanovas Garcia, Josep; Montero García, Jordi; Guasch Petit, Antonio Abstract: This paper presents experiences obtained from our involvement in the development of industrial simulation projects. Some important, common questions are covered, such as the need to define model behavior using a conceptual model, the problem of choosing the appropriate tool to code the model, and the validation and verification process required. As we will see, the scope of applicability of simulation is broad and the tools are therefore diverse. A clear understanding of the objectives of the simulation, the client’s aims and the resources at our disposal are key issues that often determine the success of a simulation project.

Post-processing: bridging the gap between modelling and effective decision-support. The Profile Assessment Grid in Human Behaviour

Fri, 22 Mar 2013 10:23:55 GMT

Title: Post-processing: bridging the gap between modelling and effective decision-support. The Profile Assessment Grid in Human Behaviour Authors: Gibert Oliveras, Karina; Rodríguez Silva, Gustavo; Annicchiarico, Roberta Abstract: The importance of post-processing the results of clustering when using data mining to support subsequent decision-making is discussed. Both the formal embedded binary logistic regression (EBLR) and the visual profile’s assessment grid (PAG) methods are presented as bridging tools for the real use of clustering results. EBLR is a sequence of logistic regressions that helps to predict the class of a new object; while PAG is a graphical tool that visualises the results of an EBLR. PAG interactively determines the most suitable class for a new object and enables subsequent follow-ups. PAG makes the underlying mathematical model (EBLR) more understandable, improves usability and contributes to bridging the gap between modelling and decision-support. When applied to medical problems, these tools can perform as diagnostic-support tools, provided that the predefined set of profiles refer to different stages of a certain disease or different types of patients with a same medical problem, etc. Being a graphical tool, PAG enables doctors to quickly and friendly determine the profile of a patient in the everyday activity, without necessarily understanding the statistical models involved in the process, which used to be a serious limitation for wider application of these methods in clinical praxis. In this work, an application is presented with 4 functional disability profiles.

A new optimal electricity market bid model solved through perspective cuts

Mon, 18 Mar 2013 12:33:44 GMT

Title: A new optimal electricity market bid model solved through perspective cuts Authors: Corchero García, Cristina; Mijangos Fernández, Eugenio; Heredia, F.-Javier (Francisco Javier) Abstract: On current electricity markets the electrical utilities are faced with very sophisticated decision making problems under uncertainty. Moreover, when focusing in the short-term management, generation companies must include some medium-term products that directly influence their short-term strategies. In this work, the bilateral and physical futures contracts are included into the day-ahead market bid following MIBEL rules and a stochastic quadratic mixed-integer programming model is presented. The complexity of this stochastic programming problem makes unpractical the resolution of large-scale instances with general-purpose optimization codes. Therefore, in order to gain efficiency, a polyhedral outer approximation of the quadratic objective function obtained by means of perspective cuts (PC) is proposed. A set of instances of the problem has been defined with real data and solved with the PC methodology. The numerical results obtained show the efficiency of this methodology compared with standard mixed quadratic optimization solvers.

An approach to disaggregating total household water consumption into major end-uses

Tue, 19 Feb 2013 11:37:54 GMT

Title: An approach to disaggregating total household water consumption into major end-uses Authors: Fontdecaba Rigat, Sara; Sánchez Espigares, Josep Anton; Marco Almagro, Lluís; Tort-Martorell Llabrés, Xavier; Cabrespina, Francesc; Zubelzu, Jordi Abstract: The aim of this project is to assign domestic water consumption to different devices based on the information provided by the water meter. We monitored a sample of Barcelona and Murcia with flow switches that recorded when a particular device was in use. In addition, the water meter readings were recorded every 5 and 1 s, respectively, in Barcelona and Murcia. The initial work used Barcelona data, and the method was later verified and adjusted with the Murcia data. The proposed method employs an algorithm that characterizes the water consumption of each device, using Barcelona to establish the initial parameters which, afterwards, provide information for adjusting the parameters of each household studied. Once the parameters have been adjusted, the algorithm assigns the consumption to each device. The efficacy of the assignation process is summarized in terms of: sensitivity and specificity. The algorithm provides a correct identification rate of between 70 % and 80 %; sometimes even higher, depending on how well the chosen parameters reflect household consumption patterns. Considering the high variability of the patterns and the fact that use is characterized by only the aggregate consumption that the water meter provides, the results are quite satisfactory.

BioStatNet: an interdisciplinary biostatistics network

Fri, 08 Feb 2013 17:55:01 GMT

Title: BioStatNet: an interdisciplinary biostatistics network Authors: Bayarri García, María Jesús; Cadarso Suárez, Carmen; Durbán Reguera, María Luz; Gómez Melis, Guadalupe; López Fidalgo, Jesús; Martín Andrés, Antonio; Nuñez Antón, Vicente; Puig Casado, Pere Abstract: Biostatistics has become a major scientific component of biomedical research with a strong interdisciplinary basis. This endeavour is essentially interdisciplinary, therefore, training of future biostatisticians must focus its efforts on the development of successful mechanisms of communication and cooperation between researchers from different disciplines. The Biostatistics National Network, BioStatNet, has been created aiming to link together Spanish and foreign researchers in Biostatistics with an integrative and open attitude. It also intends to serve as a platform for the adequate training of biostatisticians as a means towards achieving effective interdisciplinarity.

Flexible geoadditive survival analysis of non-Hodgkin lymphoma in Peru

Fri, 11 Jan 2013 08:27:53 GMT

Title: Flexible geoadditive survival analysis of non-Hodgkin lymphoma in Peru Authors: Flores, Claudio; Rodríguez-Girondo, Mar; Cadarso Suárez, Carmen; Kneib, Thomas; Gómez Melis, Guadalupe; Casanova, Lluis Abstract: Knowledge of prognostic factors is an important task for the clinical management of Non Hodgkin Lymphoma (NHL). In this work, we study the variables affecting survival of NHL in Peru by means of geoadditive Cox-type structured hazard regression models while accounting for potential spatial correlations in the survival times. We identified eight covariates with significant effect for overall survival. Some of them are widely known such as age, performance status, clinical stage and lactic dehydrogenase, but we also identified hemoglobin, leukocytes and lymphocytes as covariates with a significant effect on the overall survival of patients with NHL. Besides, the effect of continuous covariates is clearly nonlinear and hence impossible to detect with the classical Cox method. Although the spatial component does not show a significant effect, the results show a trend of low risk in certain areas.

Statistical considerations when using a composite endpoint for comparing treatment groups

Tue, 18 Dec 2012 10:53:34 GMT

Title: Statistical considerations when using a composite endpoint for comparing treatment groups Authors: Gómez Melis, Guadalupe; Lagakos, Stephen W. Abstract: When comparing two treatment groups in a time-to-event analysis, it is common to use a composite event consisting of two or more distinct outcomes. The goal of this paper is to develop a statistical methodology to derive efficiency guidelines for deciding whether to expand a study primary endpoint from E1 (for example, non-fatal myocardial infarction and cardiovascular death) to the composite of E1 and E2 (for example, non-fatal myocardial infarction, cardiovascular death or revascularisation). We investigate this problem by considering the asymptotic relative efficiency of a log-rank test for comparing treatment groups with respect to a primary relevant endpoint E1 versus the composite primary endpoint, say E , of E1 and E2, where E2 is some additional endpoint

The impact of immigration and vaccination in reducing the incidence of hepatitis B in Catalonia (Spain)

Tue, 18 Dec 2012 10:43:05 GMT

Title: The impact of immigration and vaccination in reducing the incidence of hepatitis B in Catalonia (Spain) Authors: Oviedo de La Fuente, Manuel; Muñoz Gracia, María del Pilar; Carmona, Gloria; Borras, Eva; Batalla, Joan; Soldevila, Nuria; Domínguez, Angela Abstract: Background The Hepatitis B virus (HBV) infection is a major cause of liver disease and liver cancer worldwide according to the World Health Organization. Following acute HBV infection, 1-5% of infected healthy adults and up to 90% of infected infants become chronic carriers and have an increased risk of cirrhosis and primary hepatocellular carcinoma. The aim of this study was to investigate the relationship between the reduction in acute hepatitis B incidence and the universal vaccination programme in preadolescents in Catalonia (Spain), taking population changes into account, and to construct a model to forecast the future incidence of cases that permits the best preventive strategy to be adopted. Methods Reported acute hepatitis B incidence in Catalonia according to age, gender, vaccination coverage, percentage of immigrants and the year of report of cases was analysed. A statistical analysis was made using three models: generalized linear models (GLM) with Poisson or negative binomial distribution and a generalized additive model (GAM). Results The higher the vaccination coverage, the lower the reported incidence of hepatitis B (p <0.01). In groups with vaccination coverage > 70%, the reduction in incidence was 2-fold higher than in groups with a coverage <70% (p <0.01). The increase in incidence was significantly-higher in groups with a high percentage of immigrants and more than 15% (p <0.01) in immigrant males of working age (19-49 years). Conclusions The results of the adjusted models in this study confirm that the global incidence of hepatitis B has declined in Catalonia after the introduction of the universal preadolescent vaccination programme, but the incidence increased in male immigrants of working age. Given the potential severity of hepatitis B for the health of individuals and for the community, universal vaccination programmes should continue and programmes in risk groups, especially immigrants, should be strengthened.

Multiperiod location-routing with decoupled time scales

Thu, 13 Dec 2012 16:16:36 GMT

Title: Multiperiod location-routing with decoupled time scales Authors: Albareda Sambola, Maria; Fernández Aréizaga, Elena; Nickel, Stefan Abstract: This paper focuses on a multiperiod discrete facility location problem where transportation costs are considered together with location costs to design the operating facility pattern along a time horizon. The problem captures the difference in the scope of the location and routing decisions by considering different scales within the time horizon. Thus, solutions to this problem reflect the stability of locational decisions along time. The high complexity of this problem makes it impossible to be solved in practice with commercial software. For this reason, an approximation based on replacing vehicle routes by spanning trees is proposed, and its capability for providing good quality solutions is assessed in a series of computational experiments.

Clinical Pharmacology of 3,4-Methylenedioxymethamphetamine (MDMA, "Ecstasy''): the influence of gender and genetics (CYP2D6, COMT, 5-HTT)

Tue, 11 Dec 2012 08:38:47 GMT

Title: Clinical Pharmacology of 3,4-Methylenedioxymethamphetamine (MDMA, "Ecstasy''): the influence of gender and genetics (CYP2D6, COMT, 5-HTT) Authors: Pardo-Lozano, Ricardo; Farré, Magí; Yubero-Lahoz, Samanta; O’Mathúna, Brian; Torrens, M.; Mustata, Cristina; Pérez-Mañá, Clara; Langohr, Klaus; Cuyàs, Elisabet; Carbó, Marcel·lí; de la Torre, Rafael Abstract: The synthetic psychostimulant MDMA (63,4-methylenedioxymethamphetamine, ecstasy) acts as an indirect serotonin, dopamine, and norepinephrine agonist and as a mechanism-based inhibitor of the cytochrome P-450 2D6 (CYP2D6). It has been suggested that women are more sensitive to MDMA effects than men but no clinical experimental studies have satisfactorily evaluated the factors contributing to such observations. There are no studies evaluating the influence of genetic polymorphism on the pharmacokinetics (CYP2D6; catechol-O-methyltransferase, COMT) and pharmacological effects of MDMA (serotonin transporter, 5-HTT; COMT). This clinical study was designed to evaluate the pharmacokinetics and physiological and subjective effects of MDMA considering gender and the genetic polymorphisms of CYP2D6, COMT, and 5-HTT. A total of 27 (12 women) healthy, recreational users of ecstasy were included (all extensive metabolizers for CYP2D6). A single oral weight-adjusted dose of MDMA was administered (1.4 mg/kg, range 75–100 mg) which was similar to recreational doses. None of the women were taking oral contraceptives and the experimental session was performed during the early follicular phase of their menstrual cycle. Principal findings show that subjects reached similar MDMA plasma concentrations, and experienced similar positive effects, irrespective of gender or CYP2D6 (not taking into consideration poor or ultra-rapid metabolizers) or COMT genotypes. However, HMMA plasma concentrations were linked to CYP2D6 genotype (higher with two functional alleles). Female subjects displayed more intense physiological (heart rate, and oral temperature) and negative effects (dizziness, sedation, depression, and psychotic symptoms). Genotypes of COMT val158met or 5-HTTLPR with high functionality (val/val or l/*) determined greater cardiovascular effects, and with low functionality (met/* or s/s) negative subjective effects (dizziness, anxiety, sedation). In conclusion, the contribution of MDMA pharmacokinetics following 1.4 mg/kg MDMA to the gender differences observed in drug effects appears to be negligible or even null. In contrast, 5-HTTLPR and COMT val158met genotypes play a major role.

UN ANÁLISIS DE LOS POSIBLES DETERMINANTES DE LA ASIMETRÍA DE LAS FLUCTUACIONES CÍCLICAS ENTRE LOS NUEVOS MIEMBROS DE LA UE Y LA ZONA EURO

Tue, 11 Dec 2012 08:14:44 GMT

Title: UN ANÁLISIS DE LOS POSIBLES DETERMINANTES DE LA ASIMETRÍA DE LAS FLUCTUACIONES CÍCLICAS ENTRE LOS NUEVOS MIEMBROS DE LA UE Y LA ZONA EURO Authors: Sala Ríos, Mercè; Torres Solé, Teresa; Márquez Cebrián, Dolores; Muñoz Gracia, María del Pilar Abstract: El trabajo analiza las fluctuaciones cíclicas de los nuevos miembros de la UE (PECES) en relación con las de la zona euro. El principal objetivo es averiguar si en las etapas iniciales de la liberalización del comercio e integración europea (2004-2006) los mejores resultados en la correlación de los ciclos entre los PECES y la zona euro se corresponden con los mejores resultados en las variables que según la literatura, muestran una relación más robusta con la simetría de las perturbaciones sobre la producción. Los resultados muestran que en general, la sincronización en los ciclos viene unida a una mayor intensidad comercial, especialmente de carácter intra-industrial, una menor especialización productiva, y una mayor coordinación en las principales políticas macroeconómicas.

Statistical methods in Kansei engineering: a case of statistical engineering

Tue, 23 Oct 2012 11:35:05 GMT

Title: Statistical methods in Kansei engineering: a case of statistical engineering Authors: Marco Almagro, Lluís; Tort-Martorell Llabrés, Xavier Abstract: Kansei engineering (KE) is a methodology used to incorporate emotions in products and services design. Its basic purpose is discovering in which way some properties of a product or a service convey certain emotions in its users. Data are typically collected using questionnaires. KE studies follow a model with three main steps: (i) defining the elicited emotions (semantic space); (ii) deciding on the factors that might affect the responses (space of properties); and (iii) modeling how each factor affects each response (synthesis phase). The procedure resembles that of an experimental design in an industrial context. However, practitioners of KE are hardly ever statisticians. Statistical techniques in KE are sometimes misused, and the discipline could benefit from a more extensive use of statistical methods. KE is thus a good area of application of statistical engineering: focusing not in advancement of statistics but on how current techniques can be best used in a new area. The aim of this paper is twofold: (i) to present the fundamentals of KE while giving an easy to understand example to illustrate the procedure; and (ii) to explain why KE is a good example of statistical engineering by proposing improvements that emanate from the adequate use of statistical techniques.

Principios para el análisis de la evacuación de edificios mediante redes dinámicas de flujo

Thu, 11 Oct 2012 13:15:32 GMT

Title: Principios para el análisis de la evacuación de edificios mediante redes dinámicas de flujo Authors: Casadesús Pursals, Salvador; Garriga Garzón, Federico Abstract: Para el estudio del problema de la evacuación de edificios se ha recurrido a diferentes disciplinas y a diferentes tipos de modelos. Asimismo, entre los modelos matemáticos utilizados existen numerosas posibilidades. En este trabajo se estudia la evacuación de edificios mediante redes dinámicas de flujo, que corresponden a una solución determinista en un entorno discreto. Con este modelo se dispone de la evolución de las magnitudes que caracterizan el problema en intervalos regulares de tiempo, obteniendo un conocimiento preciso y fiable del desarrollo de la evacuación, y siendo posible, además, la obtención de soluciones óptimas, las propuestas que són capaces de determinar las condiciones que minimizan tiempos de evacuación y maximizan flujos de salida.