Edición de encuestas mediante redes de neuronas artificiales

Se presenta un procedimiento de imputación de valores perdidos y un método para la detección y corrección de inconsistencias en las respuestas recogidas como resultado de una encuesta estadística. Para ello se describe el Perceptrón Multinivel, modelo concreto de Redes de Neuronas Artificiales utilizado en nuestro trabajo, y se ilustra el funcionamiento del procedimiento sobre la cuestión “Intención de voto” de una encuesta electoral del Centro de Investigaciones Sociológicas. Sobre estos datos reales, la técnica de imputación construída se basa en un modelo de predicción de la intención de voto a partir de las demás cuestiones, presentando una capacidad de generalización estimada que puede calificarse de perfecta. El modelo de detección y corrección de inconsistencias ofrece un rendimiento bastante satisfactorio, por lo que el perceptrón multinivel, confirmando algunos trabajos existentes con datos simulados, se puede considerar como un método prometedor en las tareas de edición de los registros resultantes de una encuesta estadística.Instituto de Estadística de Andalucí

e-Encuestas Probabilísticas I. Los Marcos

Se formalizan los conceptos que surgen al plantear la realización de encuestas entre los usuarios de Internet. Para ello se define el concepto de e-encuesta probabilística, que extiende la definición de encuesta probabilística al ámbito de Internet. Tras discutir algunos problemas que surgen al intentar identificar de forma unívoca a los usuarios de la Red, se describen las características más importantes de la población internauta española. Según el grado de disponibilidad de acceso a Internet, se establece una clasificación de las poblaciones objetivo de las e-encuestas probabilísticas en: Poblaciones Saturadas en Internet y Poblaciones No-Saturadas en Internet.The topics arising from Internet surveys are formalized in this work. So we define the notion of probabilistic e-survey, extending the probabilistic survey definition to the Internet field. We discuss several problems when we try to unanimously identify the Internet users, and we describe the most important characteristics of the Spanish Internetnavigate population. Considering the level of availability in Internet access, we establish a classification of target populations of the probabilistic e-surveys: Internet Saturated Populations and Internet NotSaturated Populations

Epigenetic features of human telomeres

Although subtelomeric regions in humans are heterochromatic, the epigenetic nature of human telomeres remains controversial. This controversy might have been influenced by the confounding effect of subtelomeric regions and interstitial telomeric sequences (ITSs) on telomeric chromatin structure analyses. In addition, different human cell lines might carry diverse epigenetic marks at telomeres. We have developed a reliable procedure to study the chromatin structure of human telomeres independently of subtelomeres and ITSs. This procedure is based on the statistical analysis of multiple ChIP-seq experiments. We have found that human telomeres are not enriched in the heterochromatic H3K9me3 mark in most of the common laboratory cell lines, including embryonic stem cells. Instead, they are labeled with H4K20me1 and H3K27ac, which might be established by p300. These results together with previously published data argue that subtelomeric heterochromatin might control human telomere functions. Interestingly, U2OS cells that exhibit alternative lengthening of telomeres have heterochromatic levels of H3K9me3 in their telomeres.Ministerio de Economía, Industria y Competitividad de España BIO2016–78955-PConsejo Europeo de Investigación ERC2014 AdG669898 TARLOOPMinisterio de Economía y Competitividad de España BFU2016–75058-

Triangulación de un estudio cualitativo mediante regresión logística

Fundamento y Objetivo: La investigación cualitativa complementa su visión de la realidad mediante la triangulación. La regresión logística binaria es un instrumento de predicción de riesgo en epidemiología analítica. Nuestro objetivo ha sido triangular una investigación cualitativa de tipo pedagógico con modelos de regresión logística. Material y Método: Sobre la información recogida por un grupo focal, organizamos los datos en tres variables: Aforismo / Frase corta (variable dependiente), Profesor y Tipo (variables predictoras) y construimos dos modelos con regresión logística binaria. El error alfa fue del 5 y del 10%. El tamaño muestral venía impuesto por el grupo focal anterior (saturación cualitativa). Se diseñaron rutinas para trabajar con los datos en el programa R. Resultados: Con 127 elementos (44 aforismos y 83 frases cortas) se obtuvieron significaciones crudas del 10% para dos de los diez profesores con información relevante para el grupo focal (odds ratios de 0.42 y 2.33 respectivamente; índice de Brier escalado = 0.06 y área bajo curva ROC = 0.63) y significaciones menores del 5% para cuatro de los cinco epígrafes en que habíamos dividido la variable tipo (epidemiológicos, epistemológicos, estadísticos y pragmáticos o heurísticos). El epígrafe “Estadístico” fue significativo con respecto a “Epistemológico” (OR=5,00; IC al 95% = 14.431-1.743) y con respecto a “Pragmático” (OR=4.80; IC al 95%=14.602-1.577). El epígrafe “Difusión Científica” no resultó significativo. Conclusiones: En un entorno de investigación cualitativo-pedagógica sobre aforismos y frases cortas, la regresión logística binaria se ha mostrado eficaz, dentro de una estrategia de triangulación, para identificar docentes originales para el grupo focal (p<0.10) y señalar epígrafes con interés clasificatorio (p<0.05). La capacidad predictiva de los modelos ha sido baja y la capacidad discriminativa aceptable.Background and objectives: Qualitative research seeks to enrich its vision of reality through triangulation. Binary logistic regression is a prediction tool in analytical epidemiology. Our aim was to complement a qualitative study by logistic regression models. Methods: On gathered information by a previous focus group, we organized the data into three variables: Aphorism / short phrase (dependent), Professor and Type (predictive) and built two models with binary logistic regression. The alpha error was 5 and 10%. The sample size was imposed by the previous focus group task (qualitative saturation). Routines were implemented to work with the program R. Results: With 127 elements (44 aphorisms and 83 short sentences) we obtained a 10% raw signification for two of the ten teachers with relevant information for the focus group (odds ratios of 0.42 and 2.33 respectively; Brier scaled =0.06 and area under ROC curve = 0.63) and significations less than 5% for four the five sections in which we divided the variable “Type” (epidemiological, epistemological, statistical, pragmatic or heuristic). The heading "Statistics" was significant with respect to "Epistemological" (OR = 5.00, CI 95% = 14.431-1.743) and with respect to “Pragmatic” (OR = 4.80, CI 95% = 14.602-1.577). The label "Scientific Spread" was not significant. Conclusions: In an environment of qualitative and pedagogical research on aphorisms and short phrases, binary logistic regression has been shown effective in identifying original teachers for focus group (p<0.1) and to identify qualifying entries with interest (p<0.05). The predictive capability of models has been low and acceptable the discriminative capacity.FIBAOHospital Infanta Luisa de SevillaInstituto de Salud Carlos II

Fatty acid profile as a tool to trace the origin of beef in pasture- and grain-fed young bulls of Retinta breed

This research explores the possibility of using the fatty acid profiles of intramuscular fat to authenticate the origin of Retinta breed meat according to different feeding regimes based on the combined use of concentrate and grass or forage (GP, grass pasture; MC, medium concentrate; HC, high concentrate). Young bulls from GP (n=30) were reared on grass pasture and supplement with concentrate in controlled feeders; MC (n=30) and HC (n=15) were reared in farm buildings using 40 and 80% concentrate of total dry matter from diet, respectively. The stepclass function in R was used to perform a stepwise linear discriminant analysis including thirty fatty acids from intramuscular fat. Two fatty acids, 9c18:1 and 22:5 n-3 were selected as discriminators of the meat origin. Meat from the GP and MC was characterized by higher 22:5 n-3 (p<0.05), while HC meat showed higher 9c18:1 (p<0.05). The use of 9c18:1 and 22:5 n-3 fatty acids from intramuscular fat resulted in a correct assignation of 100% of beef samples to each of the feeding regimes. Therefore, in addition to serving as an effective tool for discriminating between feeding regimes in the origin of the beef, the fatty acid profile of intramuscular fat could help companies to check the authenticity of the meat origin

Fatty acid profile as a tool to trace the origin of beef in pasture- and grain-fed young bulls of Retinta breed

This research explores the possibility of using the fatty acid profiles of intramuscular fat to authenticate the origin of Retinta breed meat according to different feeding regimes based on the combined use of concentrate and grass or forage (GP, grass pasture; MC, medium concentrate; HC, high concentrate). Young bulls from GP (n=30) were reared on grass pasture and supplement with concentrate in controlled feeders; MC (n=30) and HC (n=15) were reared in farm buildings using 40 and 80% concentrate of total dry matter from diet, respectively. The stepclass function in R was used to perform a stepwise linear discriminant analysis including thirty fatty acids from intramuscular fat. Two fatty acids, 9c18:1 and 22:5 n-3 were selected as discriminators of the meat origin. Meat from the GP and MC was characterized by higher 22:5 n-3 (p<0.05), while HC meat showed higher 9c18:1 (p<0.05). The use of 9c18:1 and 22:5 n-3 fatty acids from intramuscular fat resulted in a correct assignation of 100% of beef samples to each of the feeding regimes. Therefore, in addition to serving as an effective tool for discriminating between feeding regimes in the origin of the beef, the fatty acid profile of intramuscular fat could help companies to check the authenticity of the meat origin