Análisis de datos faltantes mediante redes neuronales artificiales

En los últimos años se ha consolidado el uso de redes neuronales artificiales como complemento a los métodos estadísticos. Sin embargo, no se ha profundizado en el estudio de cómo las redes neuronales artificiales se ven afectadas por la presencia de datos faltantes, ni en el establecimiento de las mejores estrategias para abordarlos durante la fase de análisis estadístico. En nuestro trabajo investigamos la eficacia de diversas técnicas para afrontar los datos faltantes en análisis descriptivos univariantes y en la generación de modelos de clasificación, entre las que se incluyen redes neuronales del tipo perceptrón multicapa y de función base radial. Nuestros resultados sugieren que, en general, para los tipos de variables estudiados las redes neuronales artificiales son más eficaces en la disminución del error de imputación que otras técnicas de análisis ampliamente utilizadas cuando existe un nivel de correlación no nulo con otras variables registradasIn the last years it has been consolidated the use of artificial neural nets as a complement to statistical methods. However, it has not been deeply studied neither how the presence of missing data affects artificial neuronal nets nor the establishment of the best strategies to treat missing data in the stage of statistical analysis. In our work we investigate the effectiveness of different techniques to face missing data in univariant descriptive analysis and in the generation of classification models, including multilayer perceptron and radial basis function neural nets. Our results suggest that, in general, artificial neural nets are more effective in decreasing the imputation error than other broadly used analysis technique

Method effects associated with negatively and positively worded items on the 12-item General Health Questionnaire (GHQ-12) : results from a cross-sectional survey with a representative sample of Catalonian workers

This study focused on the examination of the latent structure underlying the responses to the GHQ-12, considering the role of method effects associated with both, PW and NW items, and using two alternative parameterisations of the CFA measurement models. What should first be noted is that the studies that have included method effects in the measurement model of the GHQ-12 have been more the exception than the rule in previous research into the factor structure of this questionnaire. According to the results of the present study, we conclude that the GHQ-12 factor structure is best characterised by introducing latent method factors that capture both the method effects associated with NW and PW items (model 7). These results support the conclusion from previous research that the good fit obtained by multidimensional models (mainly the two-factor model and the three-factor Graetz's model) could simply be explained by the artificial grouping of PW and NW items. However, the interpretation of the latent (method) factors as purely integrating method bias due to wording is not straightforward. It is obvious that NW and PW items share the wording. It is also clear that this three bifactor model (one trait and two method factors) fitted the data best. And finally, there is a lot of empirical evidence on these wording effects. However, it is also relevant to discuss the large loadings of many items on the method factors, being these loadings sometimes larger than their loadings in the trait factor. The general factor explains a 52% of the shared variance, but there are some items that deserve careful attention. For example, items 3 ('playing useful part in things') and 4 ('capable of making decisions') had very low loadings on the trait factor. If we understand PW method factor as the only method bias, then it follows that these two items are purely method effects, but surely they must share some trait variance. In the same vein, items 10 ('losing confidence in yourself') and 11 ('thinking of yourself as a worthless person') load very high in the NW method factor and, as a reviewer pointed out, a likely (post-hoc) explanation is that wording bias are still confounded with a confidence/self-image factor. Therefore, the interpretation of these effects as purely method and, accordingly, the interpretation of an overall score for the scale difficult may be compromised. The second aim of this study was to examine the relationship between the method factors associated with both NW and PW items and three demographic variables, namely sex, age and educational level of the respondents. Regarding the sex, we found a statistically significant, but weak, relationship between PW and sex, so that men were more likely than women to endorse PW items. These results are in line with previous works that, in the context of RSES, have found sex differences in wording effects. 56 57 As for the explanatory role of age on method effects, we found that the relationship between age and the NW effect was not statistically significant, which supports previous research using other questionnaires (eg, self-esteem scales, 50 Hospital Anxiety & Depression Scale 64). Moreover, our results give support to previous studies which had stated that, in older adults, the strongest method effects would be associated with PW items, rather than NW items. 55 58 As to the educational level, we found that there was not a significant correlation of this variable on the two method factors. This result supports and extends the evidence obtained in Tomás et al 50 who found that the educational level of the respondents had no effect on the negative method factor using self-esteem questionnaires. This results contradicts previous research on the relationship of the NW factor and the educational level/verbal ability with different questionnaires and samples. 41 64-69 Overall, the significant effects of sex and age on trait and method factors point out that women have a worse well-being, but this effect is partly modified by a method effect on the PW items, whereas the results for age suggest that older respondents have worse well-being and this effect is magnified by a method effect on the PW factor. The results on the individual differences related to the demographic variables considered in this study cannot only help to understand the presence of wording method effects but also to identify respondents who are prone to answering PW and NW items differently. In this sense, the relationship that appears as more evident is for the age and sex variables. Another practical consequence of our study concerns the relationship between the intended measure of the GHQ-12 (ie, the GPH factor) and other constructs of interest. Several studies have shown that method effects can inflate, deflate or have no effect at all on estimates of the relationship between two constructs (see Podsakoff et al 70 for a further review of the effects that method biases have on individual measures and on the covariation between different constructs). Thus, it is desirable that both the constructs of interest as well as the effects of method factors, like PW and NW, are considered in SEM models as a means of controlling these systematic sources of bias, and thus avoiding the drawing of inaccurate conclusions about the relationship between the substantive factors. Previous research on the GHQ-12 31 36 has outlined the asymmetry in the participants' responses as a function of the wording of the items, as well as the different responses scales for the PW and NW items. This asymmetry in the participants' responses as a function of the wording of the items is consistent with results from previous research into wording effects for contrastive survey questions. 71 The extent to which the presence of method effects is linked to the asymmetric pattern of responses and/or to the different response scales for the PW and NW items in the GHQ-12 should be examined in future research. Comparing the current work with previous studies into the factorial structure of the GHQ-12, to our knowledge, this is the first study that tests a comprehensive set of models including method effects associated with both PW and NW items and also explores some demographic correlates of these method effects. Another strength of this work was the fact that it used a large representative sample of workers, but the results might not be generalised to other specific populations, for example, adolescents and elderly retired people. Twitter @jmlosilla, @VivesJ_Research Contributors All authors meet the criteria recommended by the International Committee of Medical Journal Editors (ICMJE). All authors made substantial contributions to conception and design, acquisition of data or analysis and interpretation of data. MFR and JGM: drafted the article. JV and JML: critically revised the draft for important intellectual content. JMT: worked in the statistical analysis and interpretation of data. All authors agreed on the final version. Funding This work was supported by the Grant PGC2018-100675-B-I00, Spanish Ministry of Science, Innovation and Universities (Spain). The funders had no role in the study design, data collection and analysis, decision to publish or preparation of the manuscript. Disclaimer All authors have agreed to authorship in the indicated order. All authors declare that this paper is an original unpublished work and it is not being submitted elsewhere. All authors do not have any financial interests that might be interpreted as influencing the research, and APA ethical standard were followed in the conduct of the study. Competing interests None declared. Patient consent for publication Not required. Ethics approval The research was not submitted to approval by an institutional review board since this is not a requirement at our universities for this type of study. Ethics approval was not sought for this study since this was a secondary analysis of anonymised data. Provenance and peer review Not commissioned; externally peer reviewed. Data availability statement Data are available upon reasonable request.Objective Recent studies into the factorial structure of the 12-item version of the General Health Questionnaire (GHQ-12) have shown that it was best represented by a single substantive factor when method effects associated with negatively worded (NW) items are considered. The purpose of the present study was to examine the presence of method effects, and their relationships with demographic covariates, associated with positively worded (PW) and/or NW items. Design A cross-sectional, observational study to compare a comprehensive set of confirmatory factor models, including method effects associated with PW and/or NW items with GHQ-12 responses. Setting Representative sample of all employees living in Catalonia (Spain). Participants 3050 participants (44.6% women) who responded the Second Catalonian Survey of Working Conditions. Results A confirmatory factor analysis showed that the best fitting model was a unidimensional model with two additional uncorrelated method factors associated with PW and NW items. Furthermore, structural equation modelling (SEM) revealed that method effects were differentially related to both the sex and age of the respondents. Conclusion Individual differences related to sex and age can help to identify respondents who are prone to answering PW and NW items differently. Consequently, it is desirable that both the constructs of interest as well as the effects of method factors are considered in SEM models as a means of avoiding the drawing of inaccurate conclusions about the relationships between the substantive factors

Modelado de Procesos de Neurorrehabilitación

La Neurorrehabilitación es un proceso clínico que se centra en el abordaje de la alteración del sistema nervioso. Existe una enorme variabilidad tanto en la tipología como en el grado de las lesiones neurológicas, lo que la convierte en un proceso extremadamente complejo de analizar y comprender. El presente trabajo se centra en el modelado de las principales actividades que se llevan a cabo en el contexto de la Neurorrehabilitación actual con el objetivo de detectar aquellos puntos en que puedan ser mejoradas, tanto a nivel organizativo como a nivel de ejecución. Por otra parte, se trata de comprenderlas en profundidad para tratar de transformarlas posteriormente en nuevas actividades automatizadas y monitorizadas que se ajusten al nuevo paradigma de rehabilitación ubicua, personalizada y basada en la evidencia

Identificación de Oportunidades de Mejora en Procesos de Neurorrehabilitación

El modelado de procesos es una técnica de gestión empresarial destinada a la mejora continua de los procesos de una organización, como base operativa y estructural de la misma. En el ámbito de la Neurorrehabilitación, crece el interés por los mapas de procesos como herramienta de comprensión, representación y análisis de los procesos clínicos. El presente trabajo se centra en la identificación de oportunidades de mejora de las actividades de rehabilitación, con el objetivo de definir nuevas estrategias de monitorización y automatización que permitan su evolución hacia el nuevo modelo de rehabilitación ubicua, personalizada y basada en la evidencia

IL-7/IL-7R gene variants impact circulating IL-7/IL-7R homeostasis and ART-associated immune recovery status

Altres ajuts: This study would not have been possible without the collaboration of all the patients and medical and nursing staff who have taken part in the project. This work was supported by Gilead Fellowship Program GLD14/293 and GLD17/00299 and Consejería de Economía, Innovación, Ciencia y Empleo, Junta de Andalucía (Proyecto de Investigación de Excelencia; CTS2593). YMP and ERM are supported by the Servicio Andaluz de Salud through Programa Nicolás Monardes (C-0013/17 and C-0032/17, respectively). We are also grateful to GESIDA for ''Premio para Jóvenes Investigadores 2019'' to AR. Authors greatly appreciate the comments and criticisms of the anonymous reviewers that greatly helped to improve the manuscript.A relationship between polymorphisms in genes encoding interleukin 7 (IL-7) and its cellular receptor (IL-7R) and antiretroviral therapy (ART)-associated immune recovery in HIV subjects has been previously reported. However, details of this relationship remain unclear, and the association of these polymorphisms with circulating IL-7/IL-7R levels is scarce. Here, we explored whether IL-7/IL-7R axis was associated with quantitative CD4 T-cell recovery in HIV-infected subjects. IL-7/IL-7R polymorphisms were assessed by genotyping, and multiple inheritance models were used to estimate both, their association with low pre-ART CD4 T-cell counts and incomplete immune recovery status after 48 weeks of suppressive ART. Integrated data from genetic variants association and soluble plasma IL-7/IL-7R quantification suggest that IL-7/IL-7R genotype expression could alter the homeostatic balance between soluble and membrane-bound receptors. The haplotype analyses indicates that allele combinations impacts pre-ART circulating CD4 T-cell counts, immune recovery status and the absolute increment of CD4 T-cell counts. The knowledge about how IL-7/IL-7R axis is related to quantitative CD4 T-cell recovery and immune recovery status after initiating ART could be useful regarding T-cell reservoirs investigations in HIV subjects

Design of a polishing tool for collaborative robotics using minimum viable product approach

This is an Author's Accepted Manuscript of an article published in Carlos Perez-Vidal, Luis Gracia, Samuel Sanchez-Caballero, J. Ernesto Solanes, Alessandro Saccon & Josep Tornero (2019) Design of a polishing tool for collaborative robotics using minimum viable product approach, International Journal of Computer Integrated Manufacturing, 32:9, 848-857, DOI: 10.1080/0951192X.2019.1637026 [copyright Taylor & Francis], available online at: http://www.tandfonline.com/10.1080/0951192X.2019.1637026[EN] A collaborative tool for robotic polishing is developed in this work in order to allow the simultaneous operation of the robot system and human operator to cooperatively carry out the polishing task. For this purpose, the collaborative environment is detailed and the polishing application is designed. Moreover, the polishing tool is developed and its implementation using the minimum viable product approach is obtained. Furthermore, a robust hybrid position-force control is proposed to use the developed tool attached to a robot system and some experiments are given to show its performance.This work was supported in part by the Ministerio de Ciencia e Innovacion (Spanish Government) under project [DPI2017-87656-C2-1-R] and the Generalitat Valenciana under Grant [VALi+ d APOSTD/2016/044].Perez-Vidal, C.; Gracia Calandin, LI.; Sanchez-Caballero, S.; Solanes Galbis, JE.; Saccon, A.; Tornero Montserrat, J. (2019). Design of a polishing tool for collaborative robotics using minimum viable product approach. International Journal of Computer Integrated Manufacturing. 32(9):848-857. https://doi.org/10.1080/0951192X.2019.1637026S848857329Alders, K., M. Lehe, and G. Wan. 2001. “Method for the Automatic Recognition of Surface Defects in Body Shells and Device for Carrying Out Said Method” US Patent 6,320,654, Accessed 2001 November. https://www.google.ch/patents/US6320654Alexopoulos, K., Mavrikios, D., & Chryssolouris, G. (2013). ErgoToolkit: an ergonomic analysis tool in a virtual manufacturing environment. International Journal of Computer Integrated Manufacturing, 26(5), 440-452. doi:10.1080/0951192x.2012.731610Andres, J., Gracia, L., & Tornero, J. (2011). Calibration and control of a redundant robotic workcell for milling tasks. International Journal of Computer Integrated Manufacturing, 24(6), 561-573. doi:10.1080/0951192x.2011.566284Arnal, L., Solanes, J. E., Molina, J., & Tornero, J. (2017). Detecting dings and dents on specular car body surfaces based on optical flow. Journal of Manufacturing Systems, 45, 306-321. doi:10.1016/j.jmsy.2017.07.006Blank, S. 2010. “Perfection By Subtraction - The Minimum Feature Set”. Accessed 2018 August. http://steveblank.com/2010/03/04/perfection-by-subtraction-the-minimum-feature-set/Dimeas, F., & Aspragathos, N. (2016). Online Stability in Human-Robot Cooperation with Admittance Control. IEEE Transactions on Haptics, 9(2), 267-278. doi:10.1109/toh.2016.2518670Fitzgerald, C. “Developing Baxter, A new industrial robot with common sense for U.S. manufacturing.” 2013.Gracia, L., Sala, A., & Garelli, F. (2012). A supervisory loop approach to fulfill workspace constraints in redundant robots. Robotics and Autonomous Systems, 60(1), 1-15. doi:10.1016/j.robot.2011.07.008Gracia, L., Sala, A., & Garelli, F. (2014). Robot coordination using task-priority and sliding-mode techniques. Robotics and Computer-Integrated Manufacturing, 30(1), 74-89. doi:10.1016/j.rcim.2013.08.003Gracia, L., Solanes, J. E., Muñoz-Benavent, P., Valls Miro, J., Perez-Vidal, C., & Tornero, J. (2018). Adaptive Sliding Mode Control for Robotic Surface Treatment Using Force Feedback. Mechatronics, 52, 102-118. doi:10.1016/j.mechatronics.2018.04.008Julius, R., Schürenberg, M., Schumacher, F., & Fay, A. (2017). Transformation of GRAFCET to PLC code including hierarchical structures. Control Engineering Practice, 64, 173-194. doi:10.1016/j.conengprac.2017.03.012. E. K. (2016). TOWARDS AN AUTOMATED POLISHING SYSTEM - CAPTURING MANUAL POLISHING OPERATIONS. International Journal of Research in Engineering and Technology, 05(07), 182-192. doi:10.15623/ijret.2016.0507030Khan, A. M., Yun, D., Zuhaib, K. M., Iqbal, J., Yan, R.-J., Khan, F., & Han, C. (2017). Estimation of Desired Motion Intention and compliance control for upper limb assist exoskeleton. International Journal of Control, Automation and Systems, 15(2), 802-814. doi:10.1007/s12555-015-0151-7Kirschner, D., Velik, R., Yahyanejad, S., Brandstötter, M., & Hofbaur, M. (2016). YuMi, Come and Play with Me! A Collaborative Robot for Piecing Together a Tangram Puzzle. Interactive Collaborative Robotics, 243-251. doi:10.1007/978-3-319-43955-6_29Mohammad, A. E. K., Hong, J., & Wang, D. (2018). Design of a force-controlled end-effector with low-inertia effect for robotic polishing using macro-mini robot approach. Robotics and Computer-Integrated Manufacturing, 49, 54-65. doi:10.1016/j.rcim.2017.05.011Nagata, F., Hase, T., Haga, Z., Omoto, M., & Watanabe, K. (2007). CAD/CAM-based position/force controller for a mold polishing robot. Mechatronics, 17(4-5), 207-216. doi:10.1016/j.mechatronics.2007.01.003Nakamura, Y., Hanafusa, H., & Yoshikawa, T. (1987). Task-Priority Based Redundancy Control of Robot Manipulators. The International Journal of Robotics Research, 6(2), 3-15. doi:10.1177/027836498700600201Ries, E. 2009. “What is the Minimum Viable Product”. March. Accessed 2018 August. http://venturehacks.com/articles/minimum-viable-productRobinson, F. 2001 “A Proven Methodology to Maximize Return on Risk”. Accessed 2018 August. http://www.syncdev.com/minimum-viable-productShepherd, S., & Buchstab, A. (2014). KUKA Robots On-Site. Robotic Fabrication in Architecture, Art and Design 2014, 373-380. doi:10.1007/978-3-319-04663-1_26SYMPLEXITY. “Symbiotic Human-Robot Solutions for Complex Surface Finishing Operations.” European project funded by E.U. through the H2020. Project no. 637080. Call: H2020-FoF-2014. Topic: FoF-06-2014. Starting date: 01/ 01/2015.Duration: 48 months. Accessed 2019 March. https://www.symplexity.eu/Vihlborg, P., I. Bryngelsson, B. Lindgren, L. G. Gunnarsson, and P. Graff. 2017. “Associatio between vibration exposure and hand-arm vibration symptoms in a Swedish mechanical industry.” February 2017.Vogel, J., Haddadin, S., Jarosiewicz, B., Simeral, J. D., Bacher, D., Hochberg, L. R., … van der Smagt, P. (2015). An assistive decision-and-control architecture for force-sensitive hand–arm systems driven by human–machine interfaces. 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Retrieving physical information of depolarizing systems

Light interaction with material systems may introduce depolarization to the incident light. This phenomenon comes from multiple scattering processes that take place inside the media and strongly depends on the particle characteristics. In the case of botany, plant leaves can be understood as depolarizing systems. A non-contact method to analyze these samples consist of illuminating them with well-known polarized light and study the scattered light to retrieve the physical characteristics of the sample. This physical study can be done by measuring the Mueller matrix of samples, in which the physical information of samples is encoded in their 16 elements and further mathematical treatment is required to extract the information. In the case of scattering systems, the depolarization content carries very valuable information but it is usually not inspected in the botanic field. A way to study depolarized content is by determining the so-called depolarization index P¿, which gives an overall measure of the degree of depolarization of a system but it does not measure possible anisotropic dependence of the depolarization. For instance, a depolarizer equally depolarizing any fully polarized input polarization or a depolarizer that depolarizes them in a strongly heterogenous way, may lead to the same P¿ value. In contrast, the Indices of Polarimetric Purity (IPP) are a group of metrics that further synthesize the depolarizing content, taking into account the anisotropic depolarization. In this work, we describe the main physical characteristics of samples achieved by using these IPP through plant samples. Moreover, we show how IPP highlights some structures hidden in regular intensity measurements, highlighting the potential of these metrics for botanical applications