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Pérez Martín, Jorge

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0000-0002-3588-7233
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Pérez Martín
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Jorge
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2015 - 201962020 - 20247
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Fecha de inicio: 2015 × search.filters.applied.f.itemFacultad: E.T.S. de Ingeniería Informática ×

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Mostrando 1 - 10 de 13
  • Miniatura
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    Evaluation of Markov models with discontinuities
    (Society for Medical Decision Making, 2019-02-07) Bermejo, Iñigo; Pérez Martín, Jorge; Díez Vegas, Francisco Javier
    Background. Several methods, such as the half-cycle correction and the life-table method, were developed to attenuate the error introduced in Markov models by the discretization of time. Elbasha and Chhatwal have proposed alternative “corrections” based on numerical integration techniques. They present an example whose results suggest that the trapezoidal rule, which is equivalent to the half-cycle correction, is not as accurate as Simpson’s 1/3 and 3/8 rules. However, they did not take into consideration the impact of discontinuities. Objective. To propose a method for evaluating Markov models with discontinuities. Design. Applying the trapezoidal rule, we derive a method that consists of adjusting the model by setting the cost at each point of discontinuity to the mean of the left and right limits of the cost function. We then take from the literature a model with a cycle length of 1 year and a discontinuity on the cost function and compare our method with other “corrections” using as the gold standard an equivalent model with a cycle length of 1 day. Results. As expected, for this model, the life-table method is more accurate than assuming that transitions occur at the beginning or the end of cycles. The application of numerical integration techniques without taking into account the discontinuity causes large errors. The model with averaged cost values yields very small errors, especially for the trapezoidal and the 1/3 Simpson rules. Conclusion. In the case of discontinuities, we recommend applying the trapezoidal rule on an averaged model because this method has a mathematical justification, and in our empirical evaluation, it was more accurate than the sophisticated 3/8 Simpson rule.
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    Cost-effectiveness analysis with unordered decisions
    (Elsevier, 2021-07) Díez Vegas, Francisco Javier; Luque Gallego, Manuel; Arias Calleja, Manuel; Pérez Martín, Jorge
    Introduction Cost-effectiveness analysis (CEA) is used increasingly in medicine to determine whether the health benefit of an intervention is worth the economic cost. Decision trees, the standard decision modeling technique for non-temporal domains, can only perform CEAs for very small problems. Influence diagrams can model much larger problems, but only when the decisions are totally ordered. Objective To develop a CEA method for problems with unordered or partially ordered decisions, such as finding the optimal sequence of tests for diagnosing a disease. Methods We explain how to model those problems using decision analysis networks (DANs), a new type of probabilistic graphical model, somewhat similar to Bayesian networks and influence diagrams. We present an algorithm for evaluating DANs with two criteria, cost and effectiveness, and perform some experiments to study its computational efficiency. We illustrate the representation framework and the algorithm using a hypothetical example involving two therapies and several tests and then present a DAN for a real-world problem, the mediastinal staging of non-small cell lung cancer. Results The evaluation of a DAN with two criteria, cost and effectiveness, returns a set of intervals for the willingness to pay, separated by incremental cost-effectiveness ratios (ICERs). The cost, the effectiveness, and the optimal intervention are specific for each interval, i.e., they depend on the willingness to pay. Conclusion Problems involving several unordered decisions can be modeled with DANs and evaluated in a reasonable amount of time. OpenMarkov, an open-source software tool developed by our research group, can be used to build the models and evaluate them using a graphical user interface.
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    Teaching Probabilistic Graphical Models with OpenMarkov
    (MDPI, 2022-11-30) Díez Vegas, Francisco Javier; Arias Calleja, Manuel; Pérez Martín, Jorge; Luque Gallego, Manuel
    OpenMarkov is an open-source software tool for probabilistic graphical models. It has been developed especially for medicine, but has also been used to build applications in other fields and for tuition, in more than 30 countries. In this paper we explain how to use it as a pedagogical tool to teach the main concepts of Bayesian networks and influence diagrams, such as conditional dependence and independence, d-separation, Markov blankets, explaining away, optimal policies, expected utilities, etc., and some inference algorithms: logic sampling, likelihood weighting, and arc reversal. The facilities for learning Bayesian networks interactively can be used to illustrate step by step the performance of the two basic algorithms: search-and-score and PC.
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    Cost-effectiveness of Pediatric Bilateral Cochlear Implantation in Spain
    (Wiley Online Library, 2017) Artaso, Miguel A.; Díez, Francisco Javier; Pérez Martín, Jorge
    Objective: To determine the incremental cost-effectiveness of bilateral versus unilateral cochlear implantation for one-year-old children suffering from bilateral sensorineural severe to profound hearing loss from the perspective of the Spanish public health system. Study Design: Cost-utility analysis. Methods: We conducted a general-population survey to estimate the quality of life increase contributed by the second implant. We built a Markov influence diagram and evaluated it for a life-long time horizon with a 3% discount rate in the base case. Results: The incremental cost-effectiveness ratio (ICER) of simultaneous bilateral implantation with respect to unilateral implantation for one-year-old children with severe to profound deafness is €10,323 per quality-adjusted life year (QALY). For sequential bilateral implantation, it rises to €11,733/QALY. Both options are cost-effective for the Spanish health system, whose willingness to pay is estimated at around €30,000/QALY. The probabilistic sensitivity analysis shows that the probability of bilateral implantation being cost-effective reaches 100% for that cost-effectiveness threshold. Conclusions: Bilateral implantation is clearly cost-effective for the population considered. If possible, it should be done simultaneously, i.e., in one surgical operation, because it is as safe and effective as sequential implantation, and saves costs for the system and for users and their families. Sequential implantation is also cost-effective for children who have received the first implant recently, but it is difficult to determine when it ceases to be so because of the lack of detailed data. These results are specific for Spain but the model can easily be adapted to other countries. Level of Evidence: 2C
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    Markov influence diagrams: a graphical tool for cost-effectiveness analysis
    (Society for Medical Decision Making, 2017-01-11) Yebra, Mar; Bermejo, Iñigo; Palacios Alonso, Miguel Ángel; Arias Calleja, Manuel; Luque Gallego, Manuel; Pérez Martín, Jorge; Díez Vegas, Francisco Javier
    Markov influence diagrams (MIDs) are a new type of probabilistic graphical models that extend influence diagrams in the same way as Markov decision trees extend decision trees. They have been designed to build state-transition models, mainly in medicine, and perform cost-effectiveness analysis. Using a causal graph that may contain several variables per cycle, MIDs can model various features of the patient without multiplying the number of states; in particular, they can represent the history of the patient without using tunnel states. OpenMarkov, an open-source tool, allows the decision analyst to build and evaluate MIDs—including cost-effectiveness analysis and several types of deterministic and probabilistic sensitivity analysis—with a graphical user interface, without writing any code. This way, MIDs can be used to easily build and evaluate complex models whose implementation as spreadsheets or decision trees would be cumbersome or unfeasible in practice. Furthermore, many problems that previously required discrete event simulation can be solved with MIDs, i.e., within the paradigm of state-transition models, in which many health economists feel more comfortable.
  • Miniatura
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    OpenMarkov, an Open-Source Tool for Probabilistic Graphical Models
    (International Joint Conference on Artificial Intelligence, 2019) Arias Calleja, Manuel; Pérez Martín, Jorge; Luque Gallego, Manuel; Díez Vegas, Francisco Javier
    OpenMarkov is a Java open-source tool for creating and evaluating probabilistic graphical models, including Bayesian networks, influence diagrams, and some Markov models. With more than 100,000 lines of code, it offers some features for interactive learning, explanation of reasoning, and cost-effectiveness analysis, which are not available in any other tool. OpenMarkov has been used at universities, research centers, and large companies in more than 30 countries on four continents. Several models, some of them for real-world medical applications, built with OpenMarkov, are publicly available on Internet.
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    Quality analysis of a breast thermal images database
    (Sage Journals, 2023-02-02) Sánchez Cauce, Raquel; Pérez Martín, Jorge; https://orcid.org/0000-0002-1128-3988
    The study and early detection of breast cancer are key for its treatment. We carry out an exhaustive analysis of the most used database for mastology research with infrared images, analyzing the anomalies according to five quality dimensions: completeness, correctness, concordance, plausibility, and currency. We established control queries that looked for these anomalies and that can be used to ensure the quality of the database. Finally, we briefly review the more than 40 papers that use this database and that do not mention any of these anomalies. When analyzing the database, we found 365 anomalies related to personal and clinical data, and thermal images. The errors found in our research may lead to a modification of the results and conclusions made in the articles found in the literature, serve as a basis for improvements in the quality of the database, and help future researchers to work with it.
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    Análisis de coste-efectividad en OpenMarkov. Aplicación al implante coclear bilateral pediátrico en España
    (Universidad Nacional de Educación a Distancia (España). Escuela Técnica Superior de Ingeniería Informática. Departamento de Inteligencia Artificial., 2015-10-05) Pérez Martín, Jorge; Díez Vegas, Francisco Javier
    El uso de implantes cocleares es, a día de hoy la terapia más efectiva para el tratamiento de la sordera severa y profunda. Diferentes estudios han demostrado que el implante coclear unilateral es coste-efectivo en niños y en adultos. Investigaciones recientes indican que el implante coclear bilateral (un implante en cada oído) es coste-efectivo en niños, pero el grado de incertidumbre sigue siendo elevado. El objetivo de este estudio consiste en determinar con la mayor precisión posible si el implante coclear bilateral pediátrico es coste-efectivo. Con este fin se ha construido un modelo gráfico probabilista que representa los sucesos que pueden producirse a lo largo de la vida del usuario, su impacto en la calidad de vida y los costes asociados, distinguiendo los costes que cubre el sistema nacional de sanidad de los que en España asumen los usuarios y sus familias. La construcción y la evaluación del modelo se han realizado con la herramienta de software libre OpenMarkov, desarrollada en Centro de Investigación sobre Sistemas Inteligentes de Ayuda a la Decisión (CISIAD) de la UNED, para lo cual se han añadido nuevas funcionalidades y se han extendido algunas de las ya existentes. Varios estudios han estimado que la disposición a pagar (también conocida como “umbral de coste-efectividad”) implícitamente utilizada por el sistema de sanidad español si sitúa entre entre 30.000 y 35.000 € por año de vida ajustado en calidad (AVAC). Según los resultados de nuestro modelo, la razón de coste-efectividad incremental (RCEI) del implante simultáneo frente al unilateral para niños de un año de edad es de 12.133 €/AVAC, lo cual implica que conviene poner dos implantes todos los que los necesitan. El análisis de sensibilidad confirma esta conclusión, pues para un umbral de 30.000 €/AVAC la probabilidad de que esta intervención sea coste-efectivo alcanza el 98 %. Incluso en el caso de que el sistema nacional de salud asumiera los costes que en nuestro país cubren actualmente las familias,la intervención seguiría siendo coste-efectiva, con una RCEI de 17.263 €/AVAC y una probabilidad del 94 %. La implantación debe hacerse de forma simultánea, es decir, en una sola operación quirúrgica, porque la implantación secuencial tiene la misma efectividad pero mayor coste para el sistema sanitario y para la familia. Nuestro modelo no es capaz de estimar la RCEI para niños mayores de un año porque la efectividad depende de muchos factores, principalmente de la edad actual, cuándo apareció la sordera, cuándo fue diagnosticada y, en su caso, cuándo se realizó el primer implante. Este modelo estará disponible públicamente para que otros investigadores puedan reproducir los resultados y adaptarlo a otros contextos. En particular, sería interesante analizar la RCEI en adultos y en otros países.
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    Assessment of Video Accessibility by Students of a MOOC on Digital Materials for All
    (Institute of Electrical and Electronics Engineers, 2021-05-21) Elisa M. Molanes López; Rodríguez Ascaso, Alejandro; Letón Molina, Emilio; Pérez Martín, Jorge; https://orcid.org/0000-0003-3217-8551
    The assessment of multimedia accessibility is a relevant, complex and time-consuming task, which takes more than simply checking whether the video has audiodescription and captions or not. In our study, we face this challenge through the: 1) involvement of a cohort of novice evaluators, who previously took part in a MOOC on the accessibility of digital content and 2) the division of the accessibility assessment into the application of a set of criteria. Two groups of novice accessibility testers were asked to evaluate the accessibility of two similar videos, one video per group. While both videos were equivalent in terms of their pedagogical content, only one of them had non-severe accessibility barriers for people with low vision and for blind people. Each participant was asked to rate qualitatively a set of statements extracted from the WCAG 2.1 success criteria, one generic statement about the video accessibility, and a set of statements on the quality perception and the aspects of personal preference. The largest differences in ratings occurred for statements whose success criteria had been improved. It was also the case for one success criterion that is understandable but hardly applicable by novice evaluators, according to the literature. However, the difference was statistically significant only for the success criterion with more salient differences between both videos. As a main conclusion, a group of novice evaluators can identify accessibility problems in videos when using specific accessibility statements.
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    Performance of students with different accessibility needs and preferences in “Design for All” MOOCs
    (Public Library of Science, 2024-03-07) Rodríguez Ascaso, Alejandro; Molanes López, Elisa M.; Jorge Pe´rez-Martı´nI; Pérez Martín, Jorge; Letón Molina, Emilio; https://orcid.org/0000-0003-3217-8551
    Recent research has shown that Massive Open Online Courses (MOOCs) create barriers for students with disabilities. Not taking into account their needs in the design, production or delivery of MOOCs may be one of the main causes behind this. It leads to poor compliance with suitable learning designs and web accessibility standards, as well as a lack of knowledge about the students’ needs. The objective of our research is to analyze the learning performance of the students in MOOCs on topics related to Design for All, offered in an Open edX-based platform. Accessibility support was conceived from the outset, including compliance of both the platform and the learning resources with the WCAG 2.1 accessibility standard, and with a subset of the principles of Universal Design for Learning. Additionally, students were consulted on their accessibility needs and preferences, following publicly available modeling schemes and previous research. From a sample of 765 students, who completed at least one of the graded assessment activities of the course, a multilevel multiple logistic regression model was fitted. Based on that model, the results indicate that: a) users of screen readers and users of captions show a statistically significant positive association with a good performance when compared to students with no preferences, with an odds ratio of, respectively, OR = 13.482 and OR = 13.701; b) students who have low vision or very low vision show a significant negative association with a good performance when compared to users of screen readers and to users of captions, with OR = 26.817 and OR = 27.254, respectively.