Miniconferências: Jovens Doutores

Miniconferência 1 (MiniConf1) – 23/10 (11:30 – 12:00)

Cause-Specific Regression Model for correlated data in the presence of competing risks and interval censoring

Palestrante: Márcio Rodrigues – Universidade Federal de Goiás (UFG)

Interval censoring might happen in survival analysis when it is only known that the survival response belongs to a time interval. Usually in survival analysis, a single cause for the occurrence of the event is considered, however, some studies may be interested in the occurrence of more than one event, called competing risks. The Cox proportional hazards model is model might be used to the cause-specific failure rate function. We propose a cause-specific regression model for correlated data and interval censoring. The cause-specific regression model is an extension of the traditional Cox regression model for each event type, in which failures of competing events are treated as censored observations. The present study was motivated by a longitudinal study conducted at the Dental Trauma Clinic at the Federal University of Minas Gerais, Brazil aiming to evaluate luxation of permantent teeth for their pulp prognosis as well as its prognostic factors. In this paper, the proposed methodology considers a GEE-type model using an independent work matrix to accommodate the presence of clusters. A Taylor series is used to approximate the log baseline hazard function in Cox proportional hazards regression. With this formulation, the likelihood ratio test can be used to select an appropriate order for the Taylor series approximation and maximum likelihood is used to estimate model parameters and provide statistical inference. The model performance was evaluated using a simulated data set and showing that the proposed methodology has good small sample properties. The proposed methodology is applied to a real dental trauma dataset.

Miniconferência 2 (MiniConf2) – 23/10 (15:00 – 15:30)

Unobserved heterogeneity for multiple repairable systems subject to competitive risks under imperfect repair

Palestrante: Éder Silva de Brito – Instituto Federal de Goiás (IFG)

In this study, we introduce models for the failure times of repairable systems, which experience failures due to different and independent causes while being influenced by unobservable effects acting on their failure processes. Furthermore, we assume that imperfect repairs are performed after each failure event to restore the system to its standard operational condition. In this sense, the proposed model combines the concept of imperfect repairs with independent competing risks linked by unobserved heterogeneity, which is shared by the failure times of each system. In addition to presenting these novel models, the objective of this work is to develop classic inferential methodologies for estimating maximum likelihood parameters and obtaining reliability prediction functions for each system based on its failure history. Real world applications of these models are conducted, demonstrating their capacity to identify the effect of repairs related to the causes of failure and the presence or absence of unobserved heterogeneity. Therefore, this research addresses a relevant issue in the field of reliability because, in addition to presenting models that extend and generalize ones in the literature, it has potential practical applicability in diverse scenarios involving repairable systems.




Miniconferência 3 (MiniConf3) – 24/10 (11:30 – 12:00)

Propriedades da distribuição a posteriori para dados censurados usando a distribuição Gama

Palestrante: Eduardo Ramos – Universidade de São Paulo (ICMC-USP)

Nesta apresentação, explorarei as propriedades da distribuição a posteriori da distribuição Gama, com um foco particular em dados censurados. Abordaremos as condições necessárias e suficientes para que priors impróprias resultem em posteriors próprias e examinaremos a finitude dos momentos a posteriori. Discutiremos os desafios da censura de dados e a aplicação de diversos priors objetivos. Apresentarei um novo estimador para dados censurados, que melhora a eficiência do algoritmo de Monte Carlo via Cadeias de Markov (MCMC). Por meio de um estudo de simulação, avaliaremos o desempenho de estimadores Bayesianos com diferentes priors. Aplicaremos nossa metodologia a um conjunto de dados do Atlas do Genoma do Câncer, com foco em adenocarcinoma de pulmão em pacientes acima de 70 anos, oferecendo insights valiosos sobre a progressão da doença e padrões de mortalidade.