Statistical model building: Background “knowledge” based on inappropriate preselection causes misspecification

Background: Statistical model building requires selection of variables for a model depending on the model's aim. In descriptive and explanatory models, a common recommendation often met in the literature is to include all variables in the model which are assumed or known to be associated with the outcome independent of their identification with data driven selection procedures. An open question is, how reliable this assumed "background knowledge" truly is. In fact, "known" predictors might be findings from preceding studies which may also have employed inappropriate model building strategies. Methods: We conducted a simulation study assessing the influence of treating variables as "known predictors" in model building when in fact this knowledge resulting from preceding studies might be insufficient. Within randomly generated preceding study data sets, model building with variable selection was conducted. A variable was subsequently considered as a "known" predictor if a predefined number of preceding studies identified it as relevant. Results: Even if several preceding studies identified a variable as a "true" predictor, this classification is often false positive. Moreover, variables not identified might still be truly predictive. This especially holds true if the preceding studies employed inappropriate selection methods such as univariable selection. Conclusions: The source of "background knowledge" should be evaluated with care. Knowledge generated on preceding studies can cause misspecification

An In-Situ EC-STM Study and DFT Modeling of the Adsorption of Glycerol on Cu(111) in NaOH Solution

International audienceOrganic coatings are often required for the protection of metals against environmental degradation. Despite their extensive use, only limited information is available on the initial stages of adsorption and formation of protective films, especially at the molecular and atomic level. As a model system for coating formation, this study investigates the adsorption of glycerol molecules on the single-crystalline Cu(111) surface. A combined electrochemical and scanning tunneling microscopy (EC-STM) study in NaOH aqueous solution enabled following the adsorption process in detail, providing molecular information on the glycerol film structure. A potential-driven adsorption of glycerol was observed, suppressing the adsorption of hydroxyl molecules and copper oxidation. The adsorbed species assembled in a nearest neighbor arrangement fitting a (√3 × √3) R30° hexagonal structure with respect to the Cu(111) lattice. This experimentally observed configuration was confirmed by density functional theory (DFT) calculations. DFT modeling indicates that a mixed adsorption mode involving the two primary alcohol groups adsorbed at different z-positions relative to the surface is the most favorable. This mixed configuration enabled the formation of an extended network of hydrogen bonds that aids to stabilize the glycerol film. This implies that interactions between glycerol molecules play a non-negligible effect in the growth process of such an organic film, allowing the formation of organic layers in the absence of strong interfacial interactions

Identificación de genotipos estables en 19 familias de Prosopis alba usando marcadores de microsatélites y parámetros de productividad = Identifying stable genotypes in 19 families of Prosopis alba using microsatellite markers and productivity parameters

Se caracterizaron mediante marcadores moleculares y morfométricos diecinueve familias de algarrobo blanco, de la colección a campo de Prosopis establecida en el año 2010, pertenecientes al banco de germoplasma INTA-Sáenz Peña, seleccionando la procedencia Río Bermejito (Departamento General Güemes, Chaco) por su estabilidad genética. La investigación fue conducida en la EEA (Estación Experimental Agropecuaria) INTA (Instituto Nacional de Tecnología Agropecuaria), Sáenz Peña (Latitud Sur 26º 47' 27" y Longitud Oeste 60º 26' 29"; Altitud 90 m s.n.m.), Chaco. Durante 2014-2016. Se realizó la caracterización molecular con catorce marcadores microsatélites (SSRs) y la caracterización morfológica se llevó a cabo analizando distintas variables morfométricas. Al estudiar la similitud genética entre las diecinueve familias se observó que las progenies se relacionaron en un solo grupo con un 45 % de similitud sin agruparse por familia. El estudio de la diversidad genética reveló una frecuencia alélica similar entre las familias. Además, el valor de la heterocigosidad esperada (He) resultó más baja que la heterocigosidad observada (Ho) indicando endogamia. El AMOVA y los estadísticos F de Wright evidenciaron que la mayor diferenciación genética se encuentra dentro de cada familia y es menor entre familias. La plantación presenta un distanciamiento de 4 m x 4 m con cuatro (4) pseudorepeticiones por familia. Se aplicó un análisis estadístico descriptivo y un análisis de la variancia no paramétrico Kruskal Wallis al 5 %, ambos mostraron que no existen diferencias significativas entre las familias, siendo la altura total el parámetro más estable. Este estudio permitirá un primer paso en la selección de genotipos estables para mejoramiento genético convencional.Nineteen (19) white carob families from Rio Bermejito (General Güemes Department in the Province of Chaco) belonging to the field collection of Prosopis established in 2010 were selected from the INTA-Saenz Peña germplasm bank due to their genetic stability and characterized by molecular and morphometric markers. This work was conducted in the Agricultural Experimental Station (EEA in Spanish) of the National Institute of Agricultural Technology (INTA in Spanish) located in Sáenz Peña (Latitude South 26º47'27" and West Length 60º26'29", Altitude 90 msn), Chaco during 2014-2016. The molecular characterization was performed using fourteen microsatellite markers (SSR) while the morphological one was carried out by analyzing different morphometric variables. When studying the genetic similarity among the 19 families, the progenies were related into a single group showing 45% of similarity without being grouped by family. The study of genetic diversity revealed similar frequency between families. Furthermore, the expected value for heterozygosity (He) was lower than the observed (Ho) which indicates inbreeding. The AMOVA and the Wright’s F statistical showed that the greatest genetic differentiation occurs within each family and it is lower among families. There is a 4 x 4 distancing in the plantation with four (4) pseudo-repetitions per family. The descriptive statistical analysis together with the nonparametric Kruskal Wallis at 5% of variance were both applied; both showed nonsignificant differences among families, being total height the most stable parameter. This study will allow a first step in the selection of stable genotypes for conventional breeding improvement be taken.EEA Sáenz PeñaFil: Klein, Lorena Marina. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Sáenz Peña; ArgentinaFil: Spoljaric, Mónica. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Sáenz Peña; ArgentinaFil: Torales, Susana Leonor. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Recursos Biológicos; Argentin

Role of SiC substrate surface on local tarnishing of deposited silver mirror stacks

International audienceThe role of the SiC substrate surface on the resistance to the local initiation of tarnishing of thin-layered silver stacks for demanding space mirror applications was studied by combined surface and interface analysis on model stack samples deposited by cathodic magnetron sputtering and submitted to accelerated aging in gaseous H2S. It is shown that suppressing the surface pores resulting from the bulk SiC material production process by surface pretreatment eliminates the high aspect ratio surface sites that are imperfectly protected by the SiO2 overcoat after the deposition of silver. The formation of channels connecting the silver layer to its environment through the failing protection layer at the surface pores and locally enabling H2S entry and Ag2S growth as columns until emergence at the stack surface is suppressed, which markedly delays tarnishing initiation and thereby preserves the optical performance. The results revealed that residual tarnishing initiation proceeds by a mechanism essentially identical in nature but involving different pathways short circuiting the protection layer and enabling H2S ingress until the silver layer. These permeation pathways are suggested to be of microstructural origin and could correspond to the incompletely coalesced intergranular boundaries of the SiO2 layer

Local Degradation Mechanisms by Tarnishing of Protected Silver Mirror Layers Studied by Combined Surface Analysis

International audienceIn this work, we addressed the local degradation mechanisms limiting the pre-launch environmental durability of thin-layered silver stacks for demanding space mirror applications. Local initiation and propagation of tarnishing were studied by combined surface and interface analysis on model stack samples consisting of thin silver layers supported on light-weight SiC substrates and protected by thin SiO2 overcoats, deposited by cathodic magnetron sputtering and submitted to accelerated aging in gaseous H2S. The results show that tarnishing is locally initiated by the formation of Ag2S columns erupting above the stack surface. Ag2S growth is promoted at high aspect ratio defects (surface pores) of the SiC substrate as a result of an imperfect protection by the SiO2 overcoat. Channels most likely connect the silver layer to its environment through the protection layer, which enables local H2S entry and Ag2S growth. The silver sulfide columns grow in number and size eventually leading to coalescence with increasing H2S exposure. In more advanced stages, tarnishing slows down owing to saturation of all pre-existing imperfectly protected sites of preferential sulfidation. However, it progresses radially at the basis of the Ag2S columns underneath the protection layer, consuming the metallic silver layer and deteriorating the protecting overcoat

Systematic review of education and practical guidance on regression modeling for medical researchers who lack a strong statistical background: Study protocol

In the last decades, statistical methodology has developed rapidly, in particular in the field of regression modeling. Multivariable regression models are applied in almost all medical research projects. Therefore, the potential impact of statistical misconceptions within this field can be enormous Indeed, the current theoretical statistical knowledge is not always adequately transferred to the current practice in medical statistics. Some medical journals have identified this problem and published isolated statistical articles and even whole series thereof. In this systematic review, we aim to assess the current level of education on regression modeling that is provided to medical researchers via series of statistical articles published in medical journals. The present manuscript is a protocol for a systematic review that aims to assess which aspects of regression modeling are covered by statistical series published in medical journals that intend to train and guide applied medical researchers with limited statistical knowledge. Statistical paper series cannot easily be summarized and identified by common keywords in an electronic search engine like Scopus. We therefore identified series by a systematic request to statistical experts who are part or related to the STRATOS Initiative (STRengthening Analytical Thinking for Observational Studies). Within each identified article, two raters will independently check the content of the articles with respect to a predefined list of key aspects related to regression modeling. The content analysis of the topic-relevant articles will be performed using a predefined report form to assess the content as objectively as possible. Any disputes will be resolved by a third reviewer. Summary analyses will identify potential methodological gaps and misconceptions that may have an important impact on the quality of analyses in medical research. This review will thus provide a basis for future guidance papers and tutorials in the field of regression modeling which will enable medical researchers 1) to interpret publications in a correct way, 2) to perform basic statistical analyses in a correct way and 3) to identify situations when the help of a statistical expert is required

Satisfaccion de empresas de la Septima Region con respecto al Programa Chile Joven

170 p.El propósito de nuestra investigación es determinar el grado de satisfacción que obtienen las empresas de la VII Region que reciben en practica a jóvenes que han realizado cursos de capacitación pertenecientes al Programa Chile Joven. Para ello, fueron aplicados dos cuestionarios. El primero, dirigido a los empresarios para determinar el nivel de conocimiento y percepción general del funcionamiento del Programa, y el segundo, a jefes directos de los jóvenes que realizaron la practica con el objetivo de determinar el desempeño laboral de estos jóvenes. Para la elaboración de estos cuestionarios se realizo un estudio exploratorio identificando los factores laborales y personales que el empresario considera como mas importantes para el desempeño laboral de una persona. Con esto pudo ser realizado un estudio descriptivo concluyente, cuyo resultado fue la aplicación de los dos cuestionarios. El tamaño muestral de la investigación fue de 70 empresas, las que fueron agrupadas de acuerdo al área en que se clasificaron los cursos de capacitación: administración, industrial y construcción; realizados por este Programa en las ciudades de Curic6, Talca y Linares durante los anos 1995 y 1996 periodo de estudio pertenecientes a la modalidad de trabajo dependiente. Los resultados del estudio, arrojaron con respecto al nivel de conocimiento y percepción de los empresarios hacia el Programa Chile Joven, que el 50% de estos esta satisfecho y un 19% muy satisfecho, y que además un 98,3% hot recomienda a otros, por lo tanto se concluye que hay una percepción positiva frente al Programa. El principal motivo que lleva a empresario a recibir a jóvenes en practica del programa fue ampliamente "dar oportunidad a los jóvenes" con un 58,6%, lo que demuestra que el empresario esta interesado en apoyar a los jóvenes de escasos recursos dándoles la oportunidad de realizar la practica en su empresa. A pesar que un 56,9% de los empresarios están satisfechos y un 20,7% muy satisfecho con el desempeño general del joven practicante, los jefes directos consideran que la mayoría de estos llegan a realizar su practica con pocos conocimientos, falta de experiencia y confianza en si mismo pero con un gran interés y ganas de superarse. De acuerdo a las exigencias laborales y personales impuestas por los empresarios, la mayoría de estos son cumplidas por el joven, respaldado con un 70,7% de los empresarios que señalaron que los cursos de capacitación realizados se adaptan a sus necesidades. Al determinar la coherencia entre el curso realizado por el joven y el trabajo desempeñado durante la practica, los resultados muestran que un 84,5% de los jefes directos señalo que el trabajo definitivamente si se relacionaba con el curso realizado.Del total de empresas encuestadas en la investigación, un 32,8% de ellas contrato al joven que realizo la practica en sus dependencias y un 67,2% no lo hizo, señalando como motivo de esto "no ser necesario" y "no tener presupuesto" para hacerlo

Supplementation with green tea and oregano extracts on productive characteristics, blood metabolites, and antioxidant status of Jersey cows during the transition period

Plant extracts have been recognized as beneficial to human health and have been evaluated as feed additive for domestic and companion animals. This study evaluated oregano and green tea extracts fed to Jersey cows from approximately 21 d before calving to 21 d after calving on milk production, milk composition, and blood metabolites as well as investigated immunological and antioxidant attributes. Twenty-four Jersey cows with 441±27 kg of BW, 3.5±0.3 of body condition score (BCS), and 2.7±1.8 lactations were selected at approximately 28d before the expected parturition date and were randomly assigned to three treatments with eight cows each: without plant extracts in diet (control – CON), addition of 10g per day of oregano extract (OR), and addition of 5g per day of green tea extract (GT). Feed intake, BW, BCS, blood metabolites, hemogram as well as oxidative stress biomarkers were evaluated from approximately 3 weeks prepartum to 3 weeks postpartum (transition period) while milk production and composition were evaluated during the first 3 weeks of lactation. Plant extracts did not change BW, BCS, and DM intake (DMI) throughout the transition period, but OR increased in approximately 20% total digestive nutrients and metabolizable energy intake on days 15 and 16 postpartum compared with CON. In the prepartum, OR increased in 48% platelets count compared to the CON, while GT augmented in 142% eosinophils compared with CON. Oregano extract reduced the levels of reactive species in the erythrocytes in 40% during prepartum and postpartum compared with CON, while GT reduced its levels in 24 and 29% during prepartum and postpartum, respectively, when compared with CON. In the postpartum period, OR increased in 60% the carbonylated protein content compared with CON, while GT reduced in 45% the levels of reactive species in plasma compared with CON. During the postpartum, both extracts increased in 33% the concentration of reduced glutathione when compared with CON. Moreover, GT tended to decrease feed efficiency in 11% when compared with CON; OE reduced milk pH and somatic cell count when compared with CON. In conclusion, OE and GT did not expressively affect immunological attributes in blood but reduce some oxidative stress biomarkers without compromising productive traits of Jersey cows during the transition period

Evaluación del comportamiento de variedades transgénicas de algodón en diferentes suelos y distanciamiento

La modificación en los distanciamientos entre hileras produce cambios en la intercepción, en el transporte, en el interior del canopeo y en la calidad espectral de la radiación fotosintéticamente activa (PAR). Esta modificación impacta en la fisiología, en la morfología, en el desarrollo del canopeo y en el crecimiento de las cápsulas y fibras a través de mecanismos fisiológicos específicos. La disminución de la distancia entre hileras altera el ambiente lumínico y los recursos disponibles por planta. En este sentido es importante lograr un IAF (índice de área foliar) de 3,5 a 4,5 para hacer un uso eficiente de la radiación permitiendo la iluminación de interior del canopeo (Kerby et al., 1996). El concepto de surcos estrechos y ultraestrechos ha existido desde la década de 1920 (Perkins, 1998); sin embargo, el uso de esta tecnología a nivel comercial es reciente y se aplica principalmente en Estados Unidos. En la Argentina la adopción de dicho sistema ha tenido éxito especialmente en los productores de medianos a grandes.EEA Sáenz PeñaFil: Tcach, Nydia Elisa. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Sáenz Peña; ArgentinaFil: Klein, Lorena Marina. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Sáenz Peña; ArgentinaFil: Tcach, Mauricio Alfredo. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Sáenz Peña; ArgentinaFil: Spoljaric, Mónica. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Sáenz Peña; ArgentinaFil: Gonzalez, Ariela Judith. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Sáenz Peña; Argentin