Open Access
The problem of the last bed: contextualization and a new simulation framework for analyzing physician decisions
(Elsevier, 2019) Azcárate Camio, Cristina; Esparza, Laida; Mallor Giménez, Fermín; Estadística, Informática y Matemáticas; Estatistika, Informatika eta Matematika
Faced with a full Intensive Care Unit (ICU), physicians need to decide between turning away a new patient in need of critical care and creating a vacancy by prematurely discharging a current occupant. This dilemma is widely discussed in the medical literature, where the influencing factors are identified, the patient discharge process described and the patient health consequences analyzed. Nevertheless, the existing mathematical models of ICU management practices overlook many of the factors considered by physicians in real-world triage decisions. This paper offers a review of the medical and mathematical literature on patient discharge decisions, and a proposal for a new simulation framework to enable more realistic mathematical modeling of the real-world patient discharge process. Our model includes a) the times at which discharge decisions are made and setup times for patient transfer from the ICU to a general ward and preparation of an ICU bed for an incoming patient, in order to capture the impossibility of an immediate switch of patients; b) advance notice of the number of patients due to arrive from elective surgery requiring intensive postoperative care and potentially triggering the need for early discharges to avoid surgery cancelations; and c) patient health status (to reflect the dependency of physicians’ discharge decisions on health indicators) by modeling length of stay with a phase-type distribution in which a medical meaning is assigned to each state. A simulation-based optimization method is also proposed as a means to obtain optimal discharge decisions as a function of the health status of current patients, the bed occupancy level and the number of planned arrivals from elective surgery over the following days. Optimal decisions should strike a balance between patient rejection and LoS reduction. This new simulation framework generates an optimal discharge policy, which closely resembles real decision-making under a cautious discharge policy, where the frequency of early discharge increases with the ICU occupancy level. This is a contrast with previous simulation models, which consider only the triage of the last bed, disregarding the pressures on physicians faced with high bed occupancy levels.
Open Access
Dynamic mean absolute error as new measure for assessing forecasting errors
(Elsevier, 2018-02-14) Frías Paredes, Laura; Mallor Giménez, Fermín; Gastón Romeo, Martín; León, Teresa; Estadística, Informática y Matemáticas; Estatistika, Informatika eta Matematika; Institute of Smart Cities - ISC
Accurate wind power forecast is essential for grid integration, system planning, and electricity trading in certain electricity markets. Therefore, analyzing prediction errors is a critical task that allows a comparison of prediction models and the selection of the most suitable model. In this work, the temporal error and absolute magnitude error are simultaneously considered to assess the forecast error. The trade-off between both types of errors is computed, analyzed, and interpreted. Moreover, a new index, the dynamic mean absolute error, DMAE, is defined to measure the prediction accuracy. This index accounts for both error components: temporal and absolute. Real cases of wind energy forecasting are used to illustrate the use of the new DMAE index and show the advantages of this new index over other error indices.
Open Access
Assessing energy forecasting inaccuracy by simultaneously considering temporal and absolute errors
(Elsevier, 2017-04-17) Frías Paredes, Laura; Mallor Giménez, Fermín; Gastón Romeo, Martín; León, Teresa; Estadística e Investigación Operativa; Estatistika eta Ikerketa Operatiboa; Institute of Smart Cities - ISC
Recent years have seen a growing trend in wind and solar energy generation globally and it is expected that an important percentage of total energy production comes from these energy sources. However, they present inherent variability that implies uctuations in energy generation that are dicult to forecast. Thus, forecasting errors have a considerable role in the impacts and costs of renewable energy integration, management, and commercialization. This study presents an important advance in the task of analyzing prediction models, in particular, in the timing component of prediction error, which improves previous pioneering results. A new method to match time series is dened in order to assess energy forecasting accuracy. This method relies on a new family of step patterns, an essential component of the algorithm to evaluate the temporal distortion index (TDI). This family minimizes the mean absolute error (MAE) of the transformation with respect to the reference series (the real energy series) and also allows detailed control of the temporal distortion entailed in the prediction series. The simultaneous consideration of temporal and absolute errors allows the use of Pareto frontiers as characteristic error curves. Real examples of wind energy forecasts are used to illustrate the results.
Open Access
Accumulating priority queues versus pure priority queues for managing patients in emergency departments
(Elsevier, 2019) Cildoz Esquíroz, Marta; Ibarra, Amaia; Mallor Giménez, Fermín; Institute of Smart Cities - ISC
Improving the quality of healthcare in emergency departments (EDs) is at the forefront of many hospital managers’ efforts, as they strive to plan and implement better patient flow strategies. In this paper, a new approach to manage the patient flow in EDs after triage is proposed. The new queue discipline, named accumulative priority queue with finite horizon and denoted by APQ-h, is an extension of the accumulative priority queue (APQ) discipline that considers not only the acuity level of patients and their waiting time but also the stage of the healthcare treatment. APQ disciplines have been studied in the literature from a queueing theory point of view, which requires assumptions rarely found in real EDs, such as homogeneity in the patient arrival pattern and only one service stage. The APQ-h discipline accumulates priority from the point of waiting for the first physician consultation until the moment the waiting time exceeds the upper time limit set to access the physician after the patient's arrival. A recent study shows that a management strategy of this type is applied in practice in several Canadian EDs. The main aim of this paper is to explore the implementation of APQ-h managing policies in a real ED. For this purpose, a simulation model replicating a real ED is developed. This simulation model is also used to obtain the optimal APQ type polices through a simulation-based optimization method that solves a multi-objective and stochastic optimization problem. Arrival to provider time and total waiting time in the ED are considered to be the key ED performance indicators. An extensive computational analysis shows the flexibility of the APQ-h and APQ discipline and their superiority over other pure priority disciplines in a real setting and in a variety of ED scenarios. In addition, no superiority over the APQ discipline is demonstrated. © 2019 The Authors
Open Access
Introducing the Temporal Distortion Index to perform a bidimensional analysis of renewable energy forecast
(Elsevier, 2015-11-21) Frías Paredes, Laura; Mallor Giménez, Fermín; León, Teresa; Gastón Romeo, Martín; Estadística e Investigación Operativa; Estatistika eta Ikerketa Operatiboa; Institute of Smart Cities - ISC
Wind has been the largest contributor to the growth of renewal energy during the early 21st century. However, the natural uncertainty that arises in assessing the wind resource implies the occurrence of wind power forecasting errors which perform a considerable role in the impacts and costs in the wind energy integration and its commercialization. The main goal of this paper is to provide a deeper insight in the analysis of timing errors which leads to the proposal of a new methodology for its control and measure. A new methodology, based on Dynamic TimeWarping, is proposed to be considered in the estimation of accuracy as attribute of forecast quality. A new dissimilarity measure, the Temporal Distortion Index, among time series is introduced to complement the traditional verication measures found in the literature. Furthermore we provide a bi-criteria perspective to the problem of comparing different forecasts. The methodology is illustrated with several examples including a real case.
Open Access
Simulation of household electricity consumption by using functional data analysis
(Taylor & Francis, 2018) Mallor Giménez, Fermín; Moler Cuiral, José Antonio; Urmeneta Martín-Calero, Henar; Estadística e Investigación Operativa; Estatistika eta Ikerketa Operatiboa
Open Access
Modelado de la atención en consulta externa en un hospital público: una herramienta de gestión
(Pontificia Universidad Javeriana (Colombia), 2014) Gáfaro Rojas, Aurora Inés; Mallor Giménez, Fermín; Azcárate Camio, Cristina; Estadística e Investigación Operativa; Estatistika eta Ikerketa Operatiboa
Problema: aunque se dispone de herramientas que pueden apoyar la planificación de las actividades asistenciales, hasta el momento no existe una distribución de los servicios de atención en salud cuya estructura orgánica obtenga resultados óptimos, es decir, que garantice un flujo normal de pacientes sin generar colas excesiva, con tiempos de espera adecuados, disponibilidad apropiada de personal y directrices estratégicas de programas concretos, centrados en la concepción y organización de actividades de acuerdo con la demanda de la población atendida. Objetivo: describir y aplicar una herramienta para modelar el proceso de llegadas de pacientes en un hospital colombiano, encaminado al mejoramiento de la gestión organizacional. Método: este estudio corresponde a una investigación operativa que aplica un modelo de simulación. Resultado: se generó un modelo matemático útil en otros contextos similares para la generación de llegadas o análisis de la afluencia de pacientes.
Open Access
Characterization of genetic resources of onion (Allium cepa L.) from the Spanish secondary centre of diversity
(Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA), 2011) Mallor Giménez, Cristina; Carravedo Fantova, Miguel; Estopañán Muñoz, Gloria; Mallor Giménez, Fermín; Estadística e Investigación Operativa; Estatistika eta Ikerketa Operatiboa
La cebolla es el segundo cultivo hortícola a nivel mundial. Sin embargo, el conocimiento sobre los recursos y la diversidad genética de esta especie es limitado. Por ello, el objetivo del presente trabajo consistió en el estudio morfológico y físico-químico de una colección de 86 cultivares de cebolla procedentes de España (que forma parte del centro secundario de diversificación). Los caracteres evaluados en el bulbo incluyeron: peso, forma, firmeza, contenido en sólidos solubles (SSC), pungencia y contenido en azúcares (glucosa, fructosa y sacarosa). Los resultados evidenciaron una gran variabilidad en todos los caracteres evaluados. Las correlaciones fueron significativas entre la pungencia y SSC (r = 0,34), firmeza (r = 0,32) y contenido en sacarosa (r = 0,34); entre contenido en fructosa y glucosa (r = 0,79); entre contenido en sacarosa y SSC (r = 0,57); entre SSC y peso (r = –0,35); entre contenido en fructosa y sacarosa (r = –0,22) y entre el peso y contenido en sacarosa (r = –0,43). El análisis discriminante dio lugar a la formación de cuatro grupos con un ajuste del 95,3%. El grupo 1 está formado por bulbos grandes, firmes y picantes, el grupo 2 por cebollas grandes, suaves y dulces, el grupo 3 por cebollas pequeñas, picantes y con un alto SSC y el grupo 4 por bulbos de forma alargada. La variabilidad encontrada para caracteres de interés agronómico indica que este material podría ser utilizado en futuros programas de mejora genética de esta especie. Además, la agrupación de los cultivares contribuiría a localizar mejor el material vegetal de interés y las correlaciones halladas entre los caracteres evaluados a establecer una adecuada estrategia de selección.
Open Access
Dual staining for p 167Ki67 is a more specific test than cytology for triage of HPV-positive women
(Springer, 2018) Areán Cuns, Carolina; Mercado Gutiérrez, María R.; Paniello Alastruey, Irene; Mallor Giménez, Fermín; Córdoba Iturriagagoitia, Alicia; Lozano Escario, María; Santamaría Martínez, Mercedes; Estadística, Informática y Matemáticas; Estatistika, Informatika eta Matematika
Open Access
The Temporal Distortion Index (TDI): a new procedure to analyze solar radiation forecasts
(American Institute of Physics, 2017-06-27) Gastón Romeo, Martín; Frías Paredes, Laura; Fernández-Peruchena, Carlos; Mallor Giménez, Fermín; Estadística e Investigación Operativa; Estatistika eta Ikerketa Operatiboa
In this work a new point of view to evaluate prediction models is presented. It is captured by mean of a novelty dissimilarity measure among time series, the Temporal Distortion Index (TDI), which compiles a new methodology to evaluate and control the solar radiation prediction models. This methodology complements the traditional verification measures found in the literature by adding the evaluation of the impact that time misalignments produces in the forecast accuracy. This new measure of error will allow a deeper knowledge of the prediction model behaviour besides a bi-criteria perspective to the problem of comparing different forecasts. The information about temporal features of the forecasts could play a key role in tasks as combination of different prediction models, Concentrating Solar Power (CSP) plants operation or energy grid integration.