Browsing by Author "Martins, Rui"
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- Análise Bayesiana espacial conjunta de dados longitudinais e de sobrevivência com aplicação ao estudo do VIH/SIDA no BrasilPublication . Martins, Rui; Silva, Giovani L.; Andreozzi, Valeska"A análise conjunta dos dados longitudinais e de sobrevivência tem suscitado muito interesse nos últimos anos, especialmente para dados relativos ao VIH/SIDA. Tradicionalmente, estes dados eram analisados considerando separadamente o tempo-até-evento (análise de sobrevivência) e as medições repetidas de biomarcadores (análise longitudinal). Mas, tendo em conta que os dados são observados num mesmo indivíduo, a modelação conjunta das respostas subjacentes parece ser mais apropriada. O modelo conjunto espacial bayesiano aqui proposto apresenta melhorias consideráveis nas distribuições do tempo mediano de sobrevivência quando comparado com o modelo separado."
- A Bayesian joint dispersion model with flexible linksPublication . Martins, Rui
- Bayesian joint modeling of longitudinal and spatial survival AIDS dataPublication . Martins, Rui; Silva, Giovani L.; Andreozzi, Valeska"Joint analysis of longitudinal and survival data has received increasing attention in the recent years, especially for analyzing cancer and AIDS data. As both repeated measurements (longitudinal) and time-to-event (survival) outcomes are observed in an individual, a joint modeling is more appropriate because it takes into account the dependence between the two types of responses, which are often analyzed separately. We propose a Bayesian hierarchical model for jointly modeling longitudinal and survival data considering functional time and spatial frailty effects, respectively. That is, the proposed model deals with nonlinear longitudinal effects and spatial survival effects accounting for the unobserved heterogeneity among individuals living in the same region. This joint approach is applied to a cohort study of patients with HIV/AIDS in Brazil during the years 2002–2006. Our Bayesian joint model presents considerable improvements in the estimation of survival times of the Brazilian HIV/AIDS patients when compared with those ones obtained through a separate survival model and shows that the spatial risk of death is the same across the different Brazilian states."
- Characterization of CYP2C19*17 polymorphism in a Portuguese population sample relevant for proton pump inhibitor therapy : a pilot studyPublication . Ferraz, Adriana M. L.; Bandarra, Susana; Mascarenhas, Paulo; Barahona, Isabel; Martins, Rui; Ribeiro, Ana ClaraThe interindividual variability of Proton Pump Inhibitor (PPI) therapy results from the phenotype variability associated with the cytochrome P450 2C19 (CYP2C19) gene, namely the CYP2C19*17 allele. Our aim was to characterize patients’ genetic variability undergoing PPI therapy. A sample of 33 oral mucosa cells from Portuguese pharmacy patients was collected, followed by genotyping. The allelic frequencies of CYP2C19*1 (-806C) and CYP2C19*17 (-806T) were 71.2% and 28.8%, respectively. The genotypic frequencies for CYP2C19*1/*1 and CYP2C19*1/*17 were 42.4% and 57.6%, respectively, and 19 of these patients may have a Rapid Metabolizer (RM) phenotype pharmaceutical opinion letter, based on genetic evidence.
- A crise na Ucrânia, a nova postura Russa, alterações geoestratégicas e consequências para PortugalPublication . Martins, RuiO impacto da atual crise na Ucrânia, e a ação da Rússia, sobre a estabilidade do atual Sistema Internacional, pretendeu-se, constatar a existência de consequências para Portugal, pelo seu vinculo às organizações União Europeia e Organização do Tratado do Atlântico Norte. Tendo a Rússia perdido a sua influência no Sistema Internacional logo após o fim da Guerra Fria, atualmente pretende voltar a ser um ator internacional com relevância e recuperar o estatuto de Grande Potência. Na Ucrânia, através da anexação da Crimeia em 2014 e do apoio aos separatistas no conflito a Leste, os russos impulsionaram alterações ao nível das estratégicas militar e económica das organizações ocidentais. O estudo recorreu à consulta de toda a documentação intrínseca ao enquadramento do tema, tais como, bibliografia, documentação gerada em conferências relevantes e alusivas à matéria, periódicos e outra documentação relevante. Da investigação realizada, conclui-se que, o grande impacto da crise na Ucrânia foram as alterações nas estratégias militar e económica das organizações União Europeia e Organização do Tratado do Atlântico Norte. O reforço militar, por parte da OTAN, nas fronteiras dos Aliados com a Rússia e o consequente aumento do empenhamento em missões de segurança cooperativa pelas Forças Armadas Portuguesas, demonstram as alterações da estratégia militar desta organização, face às últimas duas décadas. No caso da União Europeia a sua segurança energética e independência do gás natural russo, revelou ser de extrema importância e de resolução breve, tendo Portugal a localização geoestratégica ideal, as infraestruturas e as ligações diplomáticas, por forma a estreitar as relações com os novos fornecedores de gás natural no mundo e assim contribuir como membro europeu. Abstract: The impact of Ukraine Crisis, and Russia's action, on the stability of the current International System, was intended to note the existence of consequences to Portugal, because of his membership to the organizations European Union and North Atlantic Treaty Organization. Russia, lost her influence in the International System shortly after the end of the Cold War, intends to return to being a relevant international actor and regaining the status of Great Power. In Ukraine, by annexing the Crimea in 2014 and supporting the separatists in the Eastern conflict, the Russians pushed for changes in the military and economic strategy of Western organizations. The study pursued to consult all the documentation that is intrinsic to the theme, such as bibliography, documentation generated at relevant conferences, periodicals and other pertinent documentation. From the research, it is concluded that the major impact of the Ukraine crisis was the significant changes in the military and economic strategies of the organizations North Atlantic Treaty Organization and European Union. NATO's military reinforcement on the borders of the Allies with Russia and the consequent increase in the commitment in the cooperative security by the Portuguese Armed Forces, demonstrate the changes in the military strategy of this organization, compared to the last two decades. In the case of the European Union, its energy security and independence from Russian natural gas has proved to be extremely important and of short resolution, with Portugal having the ideal geostrategic location, infrastructure and diplomatic links, to strengthen relations with new suppliers of natural gas in the world and therefore contribute as a European member.
- Estimation of age at death from the pubic symphysis and the auricular surface of the ilium using a smoothing procedurePublication . Martins, Rui; Oliveira, Paulo Eduardo; Schmitt, Aurore"We discuss here the estimation of age at death from two indicators (pubic symphysis and the sacro-pelvic surface of the ilium) based on four different osteological series from Portugal, Great- Britain, South Africa or USA (European origin). These samples and the scoring system of the two indicators were used by Schmitt et al. (2002), applying the methodology proposed by Lucy et al. (1996). In the present work, the same data was processed using a modification of the empirical method proposed by Lucy et al. (2002). The various probability distributions are estimated from training data by using kernel density procedures and Jackknife methodology. Bayes's theorem is then used to produce the posterior distribution from which point and interval estimates may be made. This statistical approach reduces the bias of the estimates to less than 70% of what was obtained by the initial method. This reduction going up to 52% if knowledge of sex of the individual is available, and produces an age for all the individuals that improves age at death assessment."
- Joint analysis of longitudinal and survival AIDS data - a Bayesian perspectivePublication . Martins, Rui; Silva, Giovani; Andreozzi, Valeska
- Joint analysis of longitudinal and survival AIDS data with a spatial fraction of longterm survivors: a Bayesian approachPublication . Martins, Rui; Silva, Giovani; Andreozzi, Valeska
- Joint dispersion model with a flexible linkPublication . Martins, Rui"The objective is to model longitudinal and survival data jointly taking into account the dependence between the two responses in a real HIV/AIDS dataset using a shared parameter approach inside a Bayesian framework. We propose a linear mixed effects dispersion model to adjust the CD4 longitudinal biomarker data with a between-individual heterogeneity in the mean and variance. In doing so we are relaxing the usual assumption of a common variance for the longitudinal residuals. A hazard regression model is considered in addition to model the time since HIV/AIDS diagnostic until failure, being the coefficients, accounting for the linking between the longitudinal and survival processes, time-varying. This flexibility is specified using Penalized Splines and allows the relationship to vary in time. Because heteroscedasticity may be related with the survival, the standard deviation is considered as a covariate in the hazard model, thus enabling to study the effect of the CD4 counts’ stability on the survival. The proposed framework outperforms the most used joint models, highlighting the importance in correctly taking account the individual heterogeneity for the measurement errors variance and the evolution of the disease over time in bringing new insights to better understand this biomarker-survival relation."
- Joint dispersion model with a flexible linkPublication . Martins, Rui