MODESTYA

Permanent URI for this collectionhttps://hdl.handle.net/10347/34372

O traballo do grupo Modelos de Optimización, Decisión, Estatística e Aplicacións céntranse no desenvolvemento de metodoloxía estatística (estimación, contrastes, predición, optimización, etc.), cunha orientación aplicada aos ámbitos das ciencias da vida, do medio ambiente e da industria. Tamén proporciona asesoramento estatístico baixo demanda, a través do Servizo de Consultoría Estatística.

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Now showing 1 - 20 of 112

Influence of Abutment Shape on Implant Marginal Bone Remodeling: A Double-Blind, Randomized 24-Month Clinical Study
(Wiley, 2025-12-30) Seijas Naya, Flavio; Bernabeu Mira, Juan C.; Pérez Jardón, Alba; Conde Amboage, Mercedes; Peñarrocha Oltra, David; Camacho Alonso, Fabio; Pérez-Sayáns García, Mario; Universidade de Santiago de Compostela. Departamento de Estatística, Análise Matemática e Optimización; Universidade de Santiago de Compostela. Instituto de Materiais (iMATUS); Universidade de Santiago de Compostela. Departamento de Cirurxía e Especialidades Médico-Cirúrxicas
Objective This study follows a 2-year evaluation to verify marginal bone remodeling (MBR) trends associated with different abutment designs. Methods A balanced, randomised, double-blind clinical trial with two parallel experimental arms. 68 implants were placed in 9 men and 12 women, 48.5% using the straight abutment and 51.5% the concave abutment. The primary variable was peri-implant tissue stability, measured by marginal bone loss (MBL) or gain (MBG) through digital radiology. Mixed linear regression models and Additive Generalized Additive Models were constructed to estimate MBR, simultaneously considering the variables abutment height, group, and time. Results At 24 months, linear mixed-effects regression models revealed that the concave abutment group exhibited significantly less MBL than the straight abutment group across mesial, distal, and average measurements (p = 0.006–0.026). Significant interactions between abutment type and time at 8 weeks and 6 months suggest early and sustained benefits of the concave design. At 24 months, this effect remained significant except in the mesial model (p = 0.072). Abutment height was positively associated with MBL, particularly in the straight group; however, in the concave group, greater height mitigated bone loss (p < 0.01). Conclusion Concave abutments demonstrated a potential advantage in reducing early marginal bone loss and promoting mid-term bone stability compared to straight abutments. Their design may enhance soft tissue adaptation, contributing to improved peri-implant bone preservation. While increased abutment height showed a protective effect in the concave group, these findings require confirmation. Further long-term studies are warranted to validate these results and clarify their clinical relevance.
Cost allocation problems on highways with grouped users
(Elsevier, 2024-07-16) Gómez-Rodríguez, Marcos; Davila Pena, Laura; Casas Méndez, Balbina; Universidade de Santiago de Compostela. Departamento de Estatística, Análise Matemática e Optimización
One of the practical applications of cooperative transferable utility games involves determining the fee structure for users of a given facility, whose construction or maintenance costs need to be recouped. In this context, certain efficiency and equity criteria guide the considered solutions. This paper analyzes how to allocate the fixed costs of a highway among its users through tolls, considering that different classes of vehicles or travelers utilize the service. For this purpose, we make use of generalized highway games with a priori unions that represent distinct user groups, such as frequent travelers or truckers, who, due to enhanced bargaining power, often secure reductions in their fares in real-world scenarios. In particular, the Owen value, the coalitional Tijs value, and a new value termed the Shapley–Tijs value are axiomatically characterized. Additionally, straightforward formulations for calculating these values are provided. Finally, the proposed methodology is applied to actual traffic data from the AP-9 highway in Spain.
On the influence of dependent features in classification problems: A game-theoretic perspective
(Elsevier, 2025) Davila Pena, Laura; Casas Méndez, Balbina; Saavedra Nieves, Alejandro; Universidade de Santiago de Compostela. Departamento de Estatística, Análise Matemática e Optimización
This paper deals with a new measure of the influence of each feature on the outcome in classification problems, accounting for potential dependencies among certain feature subsets. Within this framework, we consider a sample of individuals characterized by specific features, each feature encompassing a finite range of values, and classified based on a binary outcome. This measure turns out to be an influence measure explored in existing literature and related to cooperative game theory. We provide an axiomatic characterization of our proposed influence measure by tailoring properties from the cooperative game theory to our specific context. Furthermore, we demonstrate that our influence measure becomes a general characterization of the well-known Banzhaf-Owen value for games with a priori unions, from the perspective of classification problems. The definitions and results presented herein are illustrated through numerical examples and various applications, offering practical insights into our methodologies.
Long-Term Study of the Changes in Symptoms and Signs of Dry Eye Disease in Participants Non-Adherent to Treatment
(MDPI, 2025-11-20) Sabucedo Villamarín, Belén; García Queiruga, Jacobo; Pena Verdeal, Hugo; Ginzo Villamayor, María José; García Resúa, Carlos; Giráldez Fernández, María Jesús; Yebra-Pimentel Vilar, Eva; Universidade de Santiago de Compostela. Departamento de Física Aplicada; Universidade de Santiago de Compostela. Departamento de Estatística, Análise Matemática e Optimización
Background: The purpose of this study was to assess differences in clinical symptoms and signs of DED in non-adherent to treatment patients to describe long-term disease progression. Methods: 120 patients previously diagnosed with Dry Eye Disease (DED) were contacted to undergo a second eye examination. The final included participants were classified into three groups based on when the second examination was scheduled: 4 years (Group 1; n = 33), 6 years (Group 2; n = 18) or 8 years (Group 3; n = 37) since the diagnostic visit. All included participants were classified as ‘non-adherent to DED treatment’, defined as patients who reported not following their prescribed DED therapy. In both examinations, Ocular Surface Disease Index (OSDI) questionnaire, tear film osmolarity, inter-eye osmolarity (osmolarity|OD-OS|), Fluorescein Break-Up Time (FBUT), Maximum Blink Interval (MBI) and corneal staining were evaluated. Results: OSDI score improved after 4 years of DED diagnosis (Group 1, mean difference close to 12 points, p < 0.001) and after 8 years (Group 3, mean difference of 9 points, p < 0.001), but remained stable after 6 years (Group 2, p = 0.328). Osmolarity worsened only after 6 years of DED diagnosis (Group 2, mean difference of 13.2 mOsm/L, p = 0.011), while osmolarity|OD–OS| showed no change (all p ≥ 0.231). FBUT values were stable across all groups (all p ≥ 0.265). MBI increased after 4 and 8 years of DED diagnosis (Groups 1 and 3, p ≤ 0.003), but not after 6 years (Group 2, p = 0.391). Corneal staining worsened after 8 years of DED diagnosis (Group 3, 0.55 points, p = 0.011), with no changes at 4 or 6 years (Groups 1 and 2, both p ≥ 0.318). Conclusions: In non-adherent DED patients, osmolarity|OD-OS| and tear film stability remain stable during the natural course of the disease, while ocular surface damage increases. However, the subjective symptomatology and the nociceptive blink reflex due to ocular discomfort decreased since the diagnostic visit.
The shapley rule for loss allocation in energy transmission networks
(Chapman and Hall/CRC (Taylor & Francis Group), 2019) Bergantiños, Gustavo; González Díaz, Julio; González Rueda, Ángel Manuel; Universidade de Santiago de Compostela. Departamento de Estatística, Análise Matemática e Optimización
We consider the problem of loss allocation in energy transmission networks. We introduce the Shapley rule defined as the Shapley value of an associated cooperative game. We study the properties satisfied by the Shapley rule. We compare this rule, in terms of the principles mentioned in the EU regulations, with the rules studied in [1]. Finally we apply this rule to the Spanish gas transmission network and carry out a simulation analysis to explore new connections between the different allocation rules.
A review on nonparametric circular regression
(Springer, 2025-05-06) Alonso Pena, María; Crujeiras Casais, Rosa María; Universidade de Santiago de Compostela. Departamento de Estatística, Análise Matemática e Optimización
Nonparametric regression models, involving circular variables (as responses and/or covariates) are revised in this chapter, focusing on a kernel approach. For linear response and circular covariate, both suitably adapted local polynomial and local likelihood models are introduced. The local polynomial approach is also presented for circular response regression. The use of these estimators for testing different hypotheses is also revised and their applicability is illustrated with a real data example. Finally, we provide some resources for the computation of the different tools.
Flexible joint modeling of mean and dispersion for the directional tuning of neuronal spike counts
(Wiley, 2023-06-16) Alonso Pena, María; Gijbels, Irene; Crujeiras Casais, Rosa María; Universidade de Santiago de Compostela. Departamento de Estatística, Análise Matemática e Optimización
The study of how the number of spikes in a MT/V5 neuron is tuned to the direction of a visual stimulus has attracted considerable attention over the years, but recent studies suggest that the variability of the number of spikes might also be influenced by the directional stimulus. This entails that Poisson regression models are not adequate for this type of data, as the observations usually present over/under-dispersion (or both) with respect to the Poisson distribution. This paper makes use of the double exponential family and presents a flexible model to estimate, jointly, the mean and dispersion functions, accounting for the effect of a circular covariate. The empirical performance of the proposal is explored via simulations and an application to a neurological dataset is shown.
Nonparametric tests for circular regression
(Taylor & Francis, 2020-09-10) Alonso Pena, María; Ameijeiras Alonso, José; Crujeiras Casais, Rosa María; Universidade de Santiago de Compostela. Departamento de Estatística, Análise Matemática e Optimización
No matter the nature of the response and/or explanatory variables in a regression model, some basic issues such as the existence of an effect of the predictor on the response, or the assessment of a common shape across groups of observations, must be solved prior to model fitting. This is also the case for regression models involving circular variables (supported on the unit circumference). In that context, using kernel regression methods, this paper provides a flexible alternative for constructing pilot estimators that allow to construct suitable statistics to perform no-effect tests and tests for equality and parallelism of regression curves. Finite sample performance of the proposed methods is analysed in a simulation study and illustrated with real data examples.
A general framework for circular local likelihood regression
(Taylor & Francis, 2023-12-21) Gijbels, Irene; Alonso Pena, María; Crujeiras Casais, Rosa María; Universidade de Santiago de Compostela. Departamento de Estatística, Análise Matemática e Optimización
This paper presents a general framework for the estimation of regression models with circular covariates, where the conditional distribution of the response given the covariate can be specified through a parametric model. The estimation of a conditional characteristic is carried out nonparametrically, by maximizing the circular local likelihood, and the estimator is shown to be asymptotically normal. The problem of selecting the smoothing parameter is also addressed, as well as bias and variance computation. The performance of the estimation method in practice is studied through an extensive simulation study, where we cover the cases of Gaussian, Bernoulli, Poisson and Gamma distributed responses. The generality of our approach is illustrated with several real-data examples from different fields.
Analyzing animal escape data with circular nonparametric multimodal regression
(Institute of Mathematical Statistics (IMS), 2023-03) Alonso Pena, María; Crujeiras Casais, Rosa María; Universidade de Santiago de Compostela. Departamento de Estatística, Análise Matemática e Optimización
Analyzing the escape direction of animals subject to covariates is a problem that requires statistical techniques beyond classical regression methods. Apart from the periodicity of the angle of direction, which demands the use of circular statistics, animal escape data usually call for the exploration of the preferred orientations rather than the expected orientation. In this paper we propose the use of a nonparametric method to estimate the conditional local modes of the escape directions of animals from a regression perspective. We present the estimation algorithms and study the asymptotic properties of the estimators as well as its finite sample performance through some simulation experiments. Our proposal is used to model the escape behavior of a group of larval zebrafish escaping from a robot predator. More broadly, the approach presented in this paper can be applied to many existing problems related to animal behavior or other fields.
Parameter estimation in ODEs: assessing the potential of local and global solvers
(Springer, 2025-06-05) Fernández de Dios, M.; González Rueda, Ángel Manuel; Rodríguez Banga, Julio; González Díaz, Julio; Rodríguez Penas, David; Universidade de Santiago de Compostela. Departamento de Estatística, Análise Matemática e Optimización
We consider the problem of parameter estimation in dynamic systems described by ordinary differential equations. A review of the existing literature emphasizes the need for deterministic global optimization methods due to the nonconvex nature of these problems. Recent works have focused on expanding the capabilities of specialized deterministic global optimization algorithms to handle more complex problems. Despite advancements, current deterministic methods are limited to problems with a maximum of around five state and five decision variables, prompting ongoing efforts to enhance their applicability to practical problems. Our study seeks to assess the effectiveness of state-of-the-art general-purpose global and local solvers in handling realistic-sized problems efficiently, and evaluating their capabilities to cope with the nonconvex nature of the underlying estimation problems.
A sampling approach for the approximation of the Deegan-Packel index
(Elsevier, 2024-07-27) Armijos-Toro, L. M.; Alonso-Meijide, J. M.; Mosquera Criado, María Jesús; Saavedra Nieves, Alejandro; Universidade de Santiago de Compostela. Departamento de Estatística, Análise Matemática e Optimización
In this paper, we address a sampling procedure for approximating the Deegan-Packel index, which is particularly advantageous when tackling with large-scale problems. It is based on the estimation of an expectation in a subdomain. Its performance is analyzed in terms of statistical properties and of bounds for the incurred absolute error. The effectiveness of this tool is demonstrated through a real-world example where this power index can be exactly computed. Finally, we use it to determine a new power distribution for two compositions of the Board of Governors of the International Monetary Fund (IMF). The resulting distributions of the power are compared with the ones prescribed by the Shapley and the Banzhaf values.
Nonparametric testing of first-order structure in point processes on linear networks
(Springer, 2025-01-27) González Pérez, Ignacio; Borrajo García, María Isabel; González Manteiga, Wenceslao; Universidade de Santiago de Compostela. Departamento de Estatística e Investigación Operativa
In this paper we address a two-sample problem in the context of point processes on linear networks. The aim is to determine whether two given point patterns defined over the same linear network and under the assumption of Poissonness, share the same spatial structure. To do so, a Kolmogorov–Smirnov and a Cramér von Mises type test statistics are developed and analysed through an extensive simulation study. We have included different types of networks, balanced and unbalanced sample sizes, and homogeneous and inhomogeneous Poisson point processes. The results show a good level adjustment and high power values, the latter increasing with the sample size and the discrepancy between the two generating intensities. Finally, these methods have also been applied to the analysis of traffic accidents in Rio de Janeiro (Brazil), studying their distribution at different rush hours.
Nonparametric First-Order Analysis of Spatial and Spatio-Temporal Point Processes
(Springer Nature, 2020-11-12) Borrajo García, María Isabel; Fuentes-Santos, I.; González Manteiga, Wenceslao; Universidade de Santiago de Compostela. Departamento de Estatística, Análise Matemática e Optimización; La Rocca, Michele; Liseo, Brunero; Salmaso, Luigi
First-order characteristics are essential functions in point processes representing the distribution of events in the corresponding domain. For decades, the inconsistency of the first-order kernel intensity estimator has been an obstacle to perform inference in the point process context. In this work, we develop different procedures to obtain consistent estimators of the first-order intensity function, and we also propose bootstrap procedures to define effective bandwidth selectors. Moreover, these innovations are used in three testing problems: the goodness-of-fit of an appealing model in the literature of point processes with covariates, the nonparametric comparison of first-order intensity functions and a separability test for spatio-temporal point process. We illustrate the above-mentioned procedures with two wildfire data sets in Galicia (NW Spain) and in Canada.
The Owen and Banzhaf-Owen values revisited
(Taylor and Francis, 2015) Alonso Meijide, José María; Casas Méndez, Balbina; González Rueda, Ángel Manuel; Lorenzo Freire, Silvia; Universidade de Santiago de Compostela. Departamento de Estatística, Análise Matemática e Optimización
In this work, we consider games with coalitional structure. We afford two new parallel axiomatic characterizations for the well-known Owen and Banzhaf–Owen coalitional values. Two properties are common to both characterizations: a property of balanced contributions and a property of neutrality. The results prove that the main difference between these two coalitional values is that the former is efficient, while the latter verifies a property of 2-efficiency.
Axiomatic of the Shapley value of a game with a priori unions
(Springer, 2014) Alonso Meijide, José María; Casas Méndez, Balbina; González Rueda, Ángel Manuel; Lorenzo Freire, Silvia; Universidade de Santiago de Compostela. Departamento de Estatística, Análise Matemática e Optimización
In this paper, we define a modification of the Shapley value for the model of TU games with a priori unions. We provide two characterizations of this value and a new characterization of the Banzhaf-Owen coalitional value.
Dynamical SPQEIR model assesses the effectiveness of non-pharmaceutical interventions against COVID-19 epidemic outbreaks
(Public Library of Science, 2021) Proverbio, Daniele; Kemp, Françoise; Magni, Stefano; Husch, Andreas; Aalto, Atte; Mombaerts, Laurent; Skupin, Alexander; Gonçalves, Jorge; Ameijeiras Alonso, José; Ley, Christophe; Universidade de Santiago de Compostela. Departamento de Estatística, Análise Matemática e Optimización
Against the current COVID-19 pandemic, governments worldwide have devised a variety of non-pharmaceutical interventions to mitigate it. However, it is generally difficult to estimate the joint impact of different control strategies. In this paper, we tackle this question with an extended epidemic SEIR model, informed by a socio-political classification of different interventions. First, we inquire the conceptual effect of mitigation parameters on the infection curve. Then, we illustrate the potential of our model to reproduce and explain empirical data from a number of countries, to perform cross-country comparisons. This gives information on the best synergies of interventions to control epidemic outbreaks while minimising impact on socio-economic needs. For instance, our results suggest that, while rapid and strong lockdown is an effective pandemic mitigation measure, a combination of social distancing and early contact tracing can achieve similar mitigation synergistically, while keeping lower isolation rates. This quantitative understanding can support the establishment of mid- and long-term interventions, to prepare containment strategies against further outbreaks. This paper also provides an online tool that allows researchers and decision makers to interactively simulate diverse scenarios with our model.
The Role of Digital Technologies in Responding to the Grand Challenges of the Natural Environment: The Windermere Accord
(Cell Press, 2021) Blair, Gordon S.; Borrajo García, María Isabel; Watkins, J.; Universidade de Santiago de Compostela. Departamento de Estatística, Análise Matemática e Optimización
Digital technology is having a major impact on many areas of society, and there is equal opportunity for impact on science. This is particularly true in the environmental sciences as we seek to understand the complexities of the natural environment under climate change. This perspective presents the outcomes of a summit in this area, a unique cross-disciplinary gathering bringing together environmental scientists, data scientists, computer scientists, social scientists, and representatives of the creative arts. The key output of this workshop is an agreed vision in the form of a framework and associated roadmap, captured in the Windermere Accord. This accord envisions a new kind of environmental science underpinned by unprecedented amounts of data, with technological advances leading to breakthroughs in taming uncertainty and complexity, and also supporting openness, transparency, and reproducibility in science. The perspective also includes a call to build an international community working in this important area.
IndexNumber: An R Package for Measuring the Evolution of Magnitudes
(The R Foundation, 2021) Saavedra Nieves, Alejandro; Saavedra Nieves, Paula; Universidade de Santiago de Compostela. Departamento de Estatística, Análise Matemática e Optimización
Index numbers are descriptive statistical measures useful in economic settings for comparing simple and complex magnitudes registered, usually in two time periods. Although this theory has a large history, it still plays an important role in modern today’s societies where big amounts of economic data are available and need to be analyzed. After a detailed revision on classical index numbers in literature, this paper is focused on the description of the R package IndexNumber with strong capabilities for calculating them. Two of the four real data sets contained in this library are used for illustrating the determination of the index numbers in this work. Graphical tools are also implemented in order to show the time evolution of considered magnitudes simplifying the interpretation of the results.
A review on specification tests for models with functional data
(INE, 2022) González Manteiga, Wenceslao; Universidade de Santiago de Compostela. Departamento de Estatística, Análise Matemática e Optimización
Nowadays, due to the progress in technological advances, massive amounts of data are generated. As a result, new statistical methodology is needed to properly manage this information. The functional data are an example of special importance. These are mainly obtained by means of high-frequency measurements (spectrometric curves, stock prices recording, etc.). Since the beginning of this century, this type of data has achieved great popularity. This fact has generated new distribution or regression models, among others, appropriate to the functional context. In the last 10 years, novel specification tests are proposed for those models. These are generalizations of methodologies developed for the vectorial framework over the last century. Besides, innovative procedures based on distance correlation ideas have been proposed as well. This article reviews the most notable developments in this context, providing some illustrations from real data sets.

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