Inferencia estadística robusta basada en divergencias para dispositivos de un sólo uso

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Matemáticas, leída el 30-06-2021A one-shot device is a unit that performs its function only once and, after use, the device either gets destroyed or must be rebuilt. For this kind of device, one can only know whether the failure time is either before or after a speci c inspection time, and consequently the lifetimes are either left- or right-censored, with the lifetime being less than the inspection time if the test outcome is a failure (resulting in left censoring) and the lifetime being more than the inspection time if the test outcome is a success (resulting in right censoring). An accelerated life test (ALT) plan is usually employed to evaluate the reliability of such products by increasing the levels of stress factors and then extrapolating the life characteristics from high stress conditions to normal operating conditions. This acceleration process will shorten the life span of devices and reduce the costs associated with the experiment. The study of one-shot device from ALT data has been developed considerably recently, mainly motivated by the work of Fan et al. [2009]...Los dispositivos de un solo uso (one shot devices en ingles), son aquellos que, una vez usados, dejan de funcionar. La mayor dificultad a la hora de modelizar su tiempo de vida es que solo se puede saber si el momento de fallo se produce antes o despues de un momento específico de inspeccion. As pues, se trata de un caso extremo de censura intervalica: si el tiempo de vida es inferior al de inspeccion observaremos un fallo (censura por la izquierda), mientras que si el tiempo de vida es mayor que el tiempo de inspeccion, observaremos un exito (censura por la derecha). Para la observacion y modelizacion de este tipo de dispositivos es comun el uso de tests de vida acelerados. Los tests de vida acelerados permiten evaluar la fiabilidad de los productos en menos tiempo, incrementando las condiciones a las que se ven sometidos los dispositivos para extrapolar despues estos resultados a condiciones mas normales. El estudio de los dispositivos de un solo uso por medio de tests de vida acelerados se ha incrementado considerablemente en los ultimos a~nos motivado, principalmente, por el trabajo de Fan et al. [2009]...Fac. de Ciencias MatemáticasTRUEunpu

Multivariate statistical techniques applied to the analysis and prediction of football matches in the main European leagues

El propósito de este estudio es analizar las estadísticas de juego en las principales ligas europeas y ver qué factores son más determinantes a la hora de predecir el resultado de un partido. Para ello usaremos técnicas de estadística multivariante incluyendo análisis de componentes principales y regresión logística. Las dos primeras componentes principales explican alrededor del 70 % de precisión obtenida cuando se predicen victorias fuera de casa tomando como variables predictivas las propias componentes. Este estudio también demuestra que en la liga inglesa los partidos son menos equilibrados.The purpose of this study is to analyse main game-related statistics differences between the main European leagues and which factors are more determinant when predicting a match score, by means of multivariate statistical techniques, including principal component analysis and logistic regression. The first two principal components explain around the 70 % of variance, and over a 70 % of accuracy is obtained when predicting away-team wins, with these two principal components as predictive variables. This study also shows that in English Premier League, games are less equilibrated.Depto. de Estadística e Investigación OperativaDepto. de Álgebra, Geometría y TopologíaFac. de Ciencias MatemáticasTRUEpu

Enseñanza del Software Estadístico R a alumnos de Matemáticas

Habiendo constatado la falta de formación en herramientas estadísticas en algunas titulaciones de matemáticas, así como la creciente importancia del software de programación R, se ha visto la necesidad de impartir un curso de Análisis de Datos con R. Éste se ha desarrollado dentro de la iniciativa “Compumates” de la Facultad de CC. Matemáticas, Universidad Complutense de Madrid, y ha constado de diferentes sesiones, que parten desde la instalación del software y uso de comandos básicos, hasta su aplicación en técnicas de análisis y predicción. Para ello se ha provisto a los alumnos de un manual de aprendizaje. En este trabajo se muestran los resultados que ha tenido la experiencia en el aprendizaje del alumno y la valoración que tiene éste sobre la misma

Teaching R to Mathematical Students

Habiendo constatado la falta de formación en herramientas estadísticas en algunas titulaciones de matemáticas, así como la creciente importancia del software de programación R, se ha visto la necesidad de impartir un curso de Análisis de Datos con R. Éste se ha desarrollado dentro de la iniciativa “Compumates” de la Facultad de CC. Matemáticas, Universidad Complutense de Madrid, y ha constado de diferentes sesiones, que parten desde la instalación del software y uso de comandos básicos, hasta su aplicación en técnicas de análisis y predicción. Para ello se ha provisto a los alumnos de un manual de aprendizaje. En este trabajo se muestran los resultados que ha tenido la experiencia en el aprendizaje del alumno y la valoración que tiene éste sobre la misma.The lack of statistical tools in some bachelor’s degrees of Mathematics jointly with an increasing importance of the software R leads to the need of giving a course of Data Analysis with R. This course has been developed under the iniciative “Compumates” of the Faculty of Mathematics at Complutense University of Madrid. It consists on different sessions that go from the basic commands to their application to techniques of analysis and prediction. In this paper, it is shown the results obtained by the students and their opinion about the course.Depto. de Estadística e Investigación OperativaDepto. de Álgebra, Geometría y TopologíaFac. de Ciencias MatemáticasTRUEpu

Robust inference for non-destructive one-shot device testing under step-stress model with exponential lifetimes

One-shot devices analysis involves an extreme case of interval censoring, wherein one can only know whether the failure time is either before or after the test time. Some kind of one-shot devices do not get destroyed when tested, and so can continue within the experiment, providing extra information for inference, if they did not fail before an inspection time. In addition, their reliability can be rapidly estimated via accelerated life tests (ALTs) by running the tests at varying and higher stress levels than working conditions. In particular, step-stress tests allow the experimenter to increase the stress levels at pre-fixed times gradually during the life-testing experiment. The cumulative exposure model is commonly assumed for step-stress models, relating the lifetime distribution of units at one stress level to the lifetime distributions at preceding stress levels. In this paper, we develop robust estimators and Z-type test statistics based on the density power divergence (DPD) for testing linear null hypothesis for non-destructive one-shot devices under the step-stress ALTs with exponential lifetime distribution. We study asymptotic and robustness properties of the estimators and test statistics, yielding point estimation and conffidence intervals for different lifetime characteristic such as reliability, distribution quantiles and mean lifetime of the devices. A simulation study is carried out to assess the performance of the methods of inference developed here and some real-life data sets are analyzed ffinally for illustrative purpose

Robust approach for comparing two dependent normal populations through Wald-type tests based on Rényi's pseudodistance estimators

Since the two seminal papers by Fisher (1915, 1921) were published, the test under a fixed value correlation coefficient null hypothesis for the bivariate normal distribution constitutes an important statistical problem. In the framework of asymptotic robust statistics, it remains being a topic of great interest to be investigated. For this and other tests, focused on paired correlated normal random samples, Rényi's pseudodistance estimators are proposed, their asymptotic distribution is established and an iterative algorithm is provided for their computation. From them the Wald-type test statistics are constructed for different problems of interest and their influence function is theoretically studied. For testing null correlation in different contexts, an extensive simulation study and two real data based examples support the robust properties of our proposal

Tutorial interactivo de ejemplos básicos y ejercicios de inferencia estadística no-paramétrica mediante software libre: implementación mediante R, R-studio y Swirl

Fac. de Comercio y TurismoFALSEsubmitte

Jejunal microvilli atrophy and reduced nutrient transport in rats with advanced liver cirrhosis: improvement by Insulin-like Growth Factor I

Es reproducción del documenteo publicado en http://dx.doi.org/10.1186/1471-230X-4-12Background: Previous results have shown that in rats with non-ascitic cirrhosis there is an altered transport of sugars and amino acids associated with elongated microvilli. These alterations returned to normal with the administration of Insulin-Like Growth Factor-I (IGF-I). The aims of this study were to explore the evolution of these alterations and analyse the effect of IGF-I in rats with advanced cirrhosis and ascites. Thus, jejunal structure and nutrient transport (D-galactose, L-leucine, L-proline, L-glutamic acid and L-cystine) were studied in rats with ascitic cirrhosis. Methods: Advanced cirrhosis was induced by CCl4 inhalation and Phenobarbital administration for 30 weeks. Cirrhotic animals were divided into two groups which received IGF-I or saline during two weeks. Control group was studied in parallel. Jejunal microvilli were studied by electron microscopy. Nutrient transport was assessed in brush border membrane vesicles using C-14 or S-35-labelled subtracts in the three experimental groups. Results: Intestinal active Na+-dependent transport was significantly reduced in untreated cirrhotic rats. Kinetic studies showed a decreased V-max and a reduced affinity for sugar and four amino acids transporters ( expressed as an increased K-t) in the brush border membrane vesicles from untreated cirrhotic rats as compared with controls. Both parameters were normalised in the IGF-I-treated cirrhotic group. Electron microscopy showed elongation and fusion of microvilli with degenerative membrane lesions and/or notable atrophy. Conclusions: The initial microvilli elongation reported in non ascitic cirrhosis develops into atrophy in rats with advanced cirrhosis and nutrient transports (monosaccharides and amino acids) are progressively reduced. Both morphological and functional alterations improved significantly with low doses of IGF-I

Tutoriales guiados de prácticas en “Estadística: Análisis de Datos e Inferencia” mediante el software libre SAS University Edition

Fac. de Comercio y TurismoFALSEsubmitte

Treatment with tocilizumab or corticosteroids for COVID-19 patients with hyperinflammatory state: a multicentre cohort study (SAM-COVID-19)

Objectives: The objective of this study was to estimate the association between tocilizumab or corticosteroids and the risk of intubation or death in patients with coronavirus disease 19 (COVID-19) with a hyperinflammatory state according to clinical and laboratory parameters. Methods: A cohort study was performed in 60 Spanish hospitals including 778 patients with COVID-19 and clinical and laboratory data indicative of a hyperinflammatory state. Treatment was mainly with tocilizumab, an intermediate-high dose of corticosteroids (IHDC), a pulse dose of corticosteroids (PDC), combination therapy, or no treatment. Primary outcome was intubation or death; follow-up was 21 days. Propensity score-adjusted estimations using Cox regression (logistic regression if needed) were calculated. Propensity scores were used as confounders, matching variables and for the inverse probability of treatment weights (IPTWs). Results: In all, 88, 117, 78 and 151 patients treated with tocilizumab, IHDC, PDC, and combination therapy, respectively, were compared with 344 untreated patients. The primary endpoint occurred in 10 (11.4%), 27 (23.1%), 12 (15.4%), 40 (25.6%) and 69 (21.1%), respectively. The IPTW-based hazard ratios (odds ratio for combination therapy) for the primary endpoint were 0.32 (95%CI 0.22-0.47; p < 0.001) for tocilizumab, 0.82 (0.71-1.30; p 0.82) for IHDC, 0.61 (0.43-0.86; p 0.006) for PDC, and 1.17 (0.86-1.58; p 0.30) for combination therapy. Other applications of the propensity score provided similar results, but were not significant for PDC. Tocilizumab was also associated with lower hazard of death alone in IPTW analysis (0.07; 0.02-0.17; p < 0.001). Conclusions: Tocilizumab might be useful in COVID-19 patients with a hyperinflammatory state and should be prioritized for randomized trials in this situatio