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2. Comparing the effectiveness of k-different treatments through the area under the ROC curve

Author

Martinez-Camblor, Pablo, Perez-Fernandez, Sonia, Dwiel, Lucas L., and Doucette, Wilder T.

Subjects
Statistics - Methodology, Statistics - Applications, Statistics - Computation
Abstract

The area under the receiver-operating characteristic curve (AUC) has become a popular index not only for measuring the overall prediction capacity of a marker but also the association strength between continuous and binary variables. In the current study, it has been used for comparing the association size of four different interventions involving impulsive decision making, studied through an animal model, in which each animal provides several negative (pre-treatment) and positive (post-treatment) measures. The problem of the full comparison of the average AUCs arises therefore in a natural way. We construct an analysis of variance (ANOVA) type test for testing the equality of the impact of these treatments measured through the respective AUCs, and considering the random-effect represented by the animal. The use (and development) of a post-hoc Tukey's HSD type test is also considered. We explore the finite-sample behavior of our proposal via Monte Carlo simulations, and analyze the data generated from the original problem. An R package implementing the procedures is provided as supplementary material.

Published
2023

4. Estimating populational-average hazard ratios in the presence of unmeasured confounding

Author

Martinez-Camblor, Pablo, MacKenzie, Todd A., and O'Malley, A. James

Subjects
Statistics - Methodology, Statistics - Applications
Abstract

The Cox regression model and its associated hazard ratio (HR) are frequently used for summarizing the effect of treatments on time to event outcomes. However, the HR's interpretation strongly depends on the assumed underlying survival model. The challenge of interpreting the HR has been the focus of a number of recent works. Besides, several alternative measures have been proposed in order to deal with these concerns. The marginal Cox regression models include an identifiable hazard ratio without individual but populational causal interpretation. In this work, we study the properties of one particular marginal Cox regression model and consider its estimation in the presence of omitted confounder. We prove the large sample consistency of an estimation score which allows non-binary treatments. Our Monte Carlo simulations suggest that finite sample behavior of the procedure is adequate. The studied estimator is more robust than its competitors for weak instruments although it is slightly more biased for large effects of the treatment. The practical use of the presented techniques is illustrated through a real practical example using data from the vascular quality initiative registry. The used R code is provided as Supplementary Material.

Published
2021

11. An Office-Based, Point-of-Care Test Predicts Treatment Outcomes With Community-Based Pelvic Floor Physical Therapy in Patients With Chronic Constipation

Author

Shah, Eric D., Pelletier, Elizabeth A., Greeley, Carol, Sieglinger, Emily E., Sanchez, Jamie D., Northam, Kayla A., Perrone, Jessica A., Curley, Michael A., Navas, Christopher M., Ostler, Tracy L., Burnett Greeley, Aimee R., Martinez-Camblor, Pablo, Baker, Jason R., Harris, Adrienne, Siegel, Corey A., and Chey, William D.

Published
2023
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13. Adjusting for bias introduced by instrumental variable estimation in the Cox Proportional Hazards Model

Author

Martinez-Camblor, Pablo, MacKenzie, Todd A., Staiger, Douglas O., Goodney, Philip P., and O'Malley, A. James

Subjects
Statistics - Methodology, 62N01, 62N02
Abstract

Instrumental variable (IV) methods are widely used for estimating average treatment effects in the presence of unmeasured confounders. However, the capability of existing IV procedures, and most notably the two-stage residual inclusion (2SRI) procedure recommended for use in nonlinear contexts, to account for unmeasured confounders in the Cox proportional hazard model is unclear. We show that instrumenting an endogenous treatment induces an unmeasured covariate, referred to as an individual frailty in survival analysis parlance, which if not accounted for leads to bias. We propose a new procedure that augments 2SRI with an individual frailty and prove that it is consistent under certain conditions. The finite sample-size behavior is studied across a broad set of conditions via Monte Carlo simulations. Finally, the proposed methodology is used to estimate the average effect of carotid endarterectomy versus carotid artery stenting on the mortality of patients suffering from carotid artery disease. Results suggest that the 2SRI-frailty estimator generally reduces the bias of both point and interval estimators compared to traditional 2SRI., Comment: 27 pages, 8 figures, 4 tables

Published
2017
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19. Dynamics of Gut Microbiota and Short-Chain Fatty Acids during a Cycling Grand Tour Are Related to Exercise Performance and Modulated by Dietary Intake

Author

Principado de Asturias, Fundación para el Fomento en Asturias de la Investigación Científica Aplicada y la Tecnología, Ministerio de Ciencia e Innovación (España), Agencia Estatal de Investigación (España), Ministerio de Ciencia, Innovación y Universidades (España), European Commission, Fernandez-Sanjurjo, Manuel, Fernández, Javier, Martínez-Camblor, Pablo, Rodriguez-Alonso, Manuel, Ortolano-Rios, Raquel, Pinto-Hernandez, Paola, Castilla-Silgado, Juan, Coto-Vilcapoma, Almudena, Ruíz García, Lorena, Villar, Claudio J., Tomas-Zapico, Cristina, Margolles Barros, Abelardo, Fernandez-Garcia, Benjamin, Iglesias-Gutiérrez, Eduardo, Lombó, Felipe, Principado de Asturias, Fundación para el Fomento en Asturias de la Investigación Científica Aplicada y la Tecnología, Ministerio de Ciencia e Innovación (España), Agencia Estatal de Investigación (España), Ministerio de Ciencia, Innovación y Universidades (España), European Commission, Fernandez-Sanjurjo, Manuel, Fernández, Javier, Martínez-Camblor, Pablo, Rodriguez-Alonso, Manuel, Ortolano-Rios, Raquel, Pinto-Hernandez, Paola, Castilla-Silgado, Juan, Coto-Vilcapoma, Almudena, Ruíz García, Lorena, Villar, Claudio J., Tomas-Zapico, Cristina, Margolles Barros, Abelardo, Fernandez-Garcia, Benjamin, Iglesias-Gutiérrez, Eduardo, and Lombó, Felipe

Abstract

Background: Regular exercise has been described to modify both the diversity and the relative abundance of certain bacterial taxa. To our knowledge, the effect of a cycling stage race, which entails extreme physiological and metabolic demands, on the gut microbiota composition and its metabolic activity has not been analysed. Objective: The aim of this cohort study was to analyse the dynamics of faecal microbiota composition and short-chain fatty acids (SCFAs) content of professional cyclists over a Grand Tour and their relationship with performance and dietary intake. Methods: 16 professional cyclists competing in La Vuelta 2019 were recruited. Faecal samples were collected at four time points: the day before the first stage (A); after 9 stages (B); after 15 stages (C); and on the last stage (D). Faecal microbiota populations and SCFA content were analysed using 16S rRNA sequencing and gas chromatography, respectively. A principal component analysis (PCA) followed by Generalised Estimating Equation (GEE) models were carried out to explore the dynamics of microbiota and SCFAs and their relationship with performance. Results: Bifidobacteriaceae, Coriobacteriaceae, Erysipelotrichaceae, and Sutterellaceae dynamics showed a strong final performance predictive value (r = 0.83, ranking, and r = 0.81, accumulated time). Positive correlations were observed between Coriobacteriaceae with acetate (r = 0.530) and isovalerate (r = 0.664) and between Bifidobacteriaceae with isobutyrate (r = 0.682). No relationship was observed between SCFAs and performance. The abundance of Erysipelotrichaceae at the beginning of La Vuelta was directly related to the previous intake of complex-carbohydrate-rich foods (r = 0.956), while during the competition, the abundance of Bifidobacteriaceae was negatively affected by the intake of simple carbohydrates from supplements (r = −0.650). Conclusions: An ecological perspective represents more realistically the relationship between gut microbiota co

Published
2024

21. Comparing the effectiveness of k$$ k $$‐different treatments through the area under the ROC curve.

Author

Martínez‐Camblor, Pablo, Pérez‐Fernández, Sonia, Dwiel, Lucas L., and Doucette, Wilder T.

Subjects
*RECEIVER operating characteristic curves, *MONTE Carlo method, *DECISION making, *CONFORMANCE testing, *ANALYSIS of variance
Abstract

The area under the receiver‐operating characteristic curve (AUC) has become a popular index not only for measuring the overall prediction capacity of a marker but also the strength of the association between continuous and binary variables. In the current considered study, the AUC was used for comparing the association size of four different interventions involving impulsive decision making, studied through an animal model, in which each animal provides several negative (pretreatment) and positive (posttreatment) measures. The problem of the full comparison of the average AUCs arises therefore in a natural way. We construct an analysis of variance (ANOVA) type test for testing the equality of the impact of these treatments measured through the respective AUCs and considering the random‐effect represented by the animal. The use (and development) of a post hoc Tukey's HSD‐type test is also considered. We explore the finite‐sample behaviour of our proposal via Monte Carlo simulations, and analyse the data generated from the original problem. An R package implementing the procedures is provided in the supporting information. [ABSTRACT FROM AUTHOR]

Published
2024
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22. Sex differences between women and men with COPD: A new analysis of the 3CIA study

Author

Perez, Tamara Alonso, Castillo, Elena García, Ancochea, Julio, Pastor Sanz, María Teresa, Almagro, Pere, Martínez-Camblor, Pablo, Miravitlles, Marc, Rodríguez-Carballeira, Mónica, Navarro, Annie, Lamprecht, Bernd, Ramírez-García Luna, Ana S., Kaiser, Bernhard, Alfageme, Inmaculada, Casanova, Ciro, Esteban, Cristóbal, Soler-Cataluña, Juan J., De-Torres, Juan P., Celli, Bartolomé R., Marin, Jose M., Lopez-Campos, Jose L., Riet, Gerben Ter, Sobradillo, Patricia, Lange, Peter, Garcia-Aymerich, Judith, Anto, Josep M., Turner, Alice M., Han, MeiLan K., Langhammer, Arnulf, Sternberg, Alice, Leivseth, Linda, Bakke, Per, Johannessen, Ane, Oga, Toru, Cosío, Borja, Echazarreta, Andres, Roche, Nicolas, Burgel, Pierre-Régis, Sin, Don D., Puhan, Milo A., and Soriano, Joan B.

Published
2020
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34. Unified ROC Curve Estimator for Diagnosis and Prognosis Studies: The sMSROC Package.

Author

Díaz-Coto, Susana, Martínez-Camblor, Pablo, and Corral-Blanco, Norberto

Subjects
*RECEIVER operating characteristic curves, *CURVE fitting, *PROGNOSIS, *DIAGNOSIS, *DECISION making
Abstract

The binary classification problem is a hot topic in Statistics. Its close relationship with the diagnosis and the prognosis of diseases makes it crucial in biomedical research. In this context, it is important to identify biomarkers that may help to classify individuals into different classes, for example, diseased vs. not diseased. The Receiver Operating-Characteristic (ROC) curve is a graphical tool commonly used to assess the accuracy of such classification. Given the diverse nature of diagnosis and prognosis problems, the ROC curve estimation has been tackled from separate perspectives in each setting. The Two-stages Mixed-Subjects (sMS) ROC curve estimator fits both scenarios. Besides, it can handle data with missing or incomplete outcome values. This paper introduces the R package sMSROC which implements the sMS ROC estimator, and includes tools that may support researchers in their decision making. Its practical application is illustrated on three real-world datasets. [ABSTRACT FROM AUTHOR]

Published
2023

42. About the use of the overlap coefficient in the binary classification context.

Author

Martínez-Camblor, Pablo

Subjects
*LEUKOCYTE count, *CEREBROSPINAL fluid examination, *BACTERIAL meningitis, *GEODETIC astronomy, *CLASSIFICATION
Abstract

The overlap coefficient (OVL) measures the common area between two or more density functions. It has been used for measuring the similarity between distributions in different research fields including astronomy, economy or sociology, among others. Recently, different authors have studied the use of the OVL coefficient in the binary classification problem. They argue that, in particular settings, it could provide better accuracy measure than other stablished indices. We prove here that the OVL coefficient does not provide additional information to the Youden index and that, the potential advantages previously reported are based on the assumption that the classification rules underlying any classification process always assign more probability of being positive to the larger values of the marker. Particularly, we prove that, for a fixed continuous marker, the OVL coefficient is equivalent to the Youden index associated with the optimal classification rules based on this marker. We illustrate the problem studying the capacity of the white blood cells count to identify the type of disease in patients having either acute viral meningitis or acute bacterial meningitis. [ABSTRACT FROM AUTHOR]

Published
2023
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44. Dynamics of gut microbiota and short-chain fatty acids during a cycling Grand Tour are related to exercise performance and modulated by dietary intake

Author

Fernández-Sanjurjo, Manuel, primary, Fernández, Javier, additional, Martínez-Camblor, Pablo, additional, Rodríguez-Alonso, Manuel, additional, Ortolano-Ríos, Raquel, additional, Pinto-Hernández, Paola, additional, Castilla-Silgado, Juan, additional, Coto-Vilcapoma, Almudena, additional, Ruiz, Lorena, additional, Villar-Granja, Claudio J, additional, Tomás-Zapico, Cristina, additional, Margolles, Abelardo, additional, Fernández-García, Benjamín, additional, Iglesias-Gutiérrez, Eduardo, additional, and Lombó, Felipe, additional

Published
2022
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46. sj-pdf-1-smm-10.1177_09622802231160053 - Supplemental material for Confidence intervals for the length of the receiver-operating characteristic curve based on a smooth estimator

Author

Martínez-Camblor, Pablo

Subjects
111099 Nursing not elsewhere classified, 111708 Health and Community Services, 160807 Sociological Methodology and Research Methods, FOS: Health sciences, FOS: Sociology
Abstract

Supplemental material, sj-pdf-1-smm-10.1177_09622802231160053 for Confidence intervals for the length of the receiver-operating characteristic curve based on a smooth estimator by Pablo Martínez-Camblor in Statistical Methods in Medical Research

Published
2023
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