Modelling longitudinal binary outcomes with outcome dependent observation times: an application to a malaria cohort study.

BACKGROUND : In spite of the global reduction of 21% in malaria incidence between 2010 and 2015, the disease still threatens many lives of children and pregnant mothers in African countries. A correct assessment and evaluation of the impact of malaria control strategies still remains quintessential in order to eliminate the disease and its burden. Malaria follow-up studies typically involve routine visits at pre-scheduled time points and/or clinical visits whenever individuals experience malaria-like symptoms. In the latter case, infection triggers outcome assessment, thereby leading to outcome-dependent sampling (ODS). Commonly used methods to analyze such longitudinal data ignore ODS and potentially lead to biased estimates of malaria-specific transmission parameters, hence, inducing an incorrect assessment and evaluation of malaria control strategies. METHODS : In this paper, a new method is proposed to handle ODS by use of a joint model for the longitudinal binary outcome measured at routine visits and the clinical event times. The methodology is applied to malaria parasitaemia data from a cohort of [Formula: see text] Ugandan children aged 0.5-10 years from 3 regions (Walukuba-300 children, Kihihi-355 children and Nagongera-333 children) with varying transmission intensities (entomological inoculation rate equal to 2.8, 32 and 310 infectious bites per unit year, respectively) collected between 2011-2014. RESULTS : The results indicate that malaria parasite prevalence and force of infection (FOI) increase with age in the region of high malaria intensity with highest FOI in age group 5-10 years. For the region of medium intensity, the prevalence slightly increases with age and the FOI for the routine process is highest in age group 5-10 years, yet for the clinical infections, the FOI gradually decreases with increasing age. For the region with low intensity, both the prevalence and FOI peak at the age of 1 year after which the former remains constant with age yet the latter suddenly decreases with age for the clinically observed infections. CONCLUSION : Malaria parasite prevalence and FOI increase with age in the region of high malaria intensity. In all study sites, both the prevalence and FOI are highest among previously asymptomatic children and lowest among their symptomatic counterparts. Using a simulation study inspired by the malaria data at hand, the proposed methodology shows to have the smallest bias, especially when consecutive positive malaria parasitaemia presence results within a time period of 35 days were considered to be due to the same infection.

Controle externo e drift institucional na Primeira República / Control externo y drift institucional en la Primera República brasileña / External control and institutional drift in the First Brazilian Republic

Resumo Esta pesquisa trata do desenvolvimento das instituições federais de controle externo durante a Primeira República brasileira. É um tema pouco visitado pela bibliografia, em geral abordado em retrospectivas que compõem estudos cujos focos estão na história recente do Tribunal de Contas da União (TCU), marcada pelo advento da Nova República (1985-). Tais estudos sugerem um padrão histórico no desenvolvimento das instituições federais de controle externo, caracterizado pela alternância entre períodos de expansão e de retração de suas atribuições. O conhecimento acerca desse padrão histórico de desenvolvimento institucional, para avançar, carece do aprofundamento das pesquisas sobre o período no qual se estabeleceram as bases de sua construção: a Primeira República. Este estudo pretende ser uma contribuição à superação dessa lacuna. Ele sustenta que o desenvolvimento das instituições federais de controle externo no período em questão foi caracterizado pela expansão legal de atribuições, de 1890 a 1892, seguida pela abdicação prática dali até 1930, por drift institucional, da responsabilidade de julgar as contas anuais de governo. O estudo é institucionalista histórico e foi construído com base na análise de fontes primárias.

Resumen Esta investigación aborda el desarrollo de las instituciones federales de control externo durante la Primera República brasileña. Es un tema es poco visitado por la bibliografía, que, en general, lo aborda en retrospectivas presentes en estudios centrados en la historia reciente del Tribunal de Cuentas de la Unión, a menudo demarcada por el advenimiento de la Nueva República (1985-actualidad). Los estudios sugieren la existencia de un patrón histórico de desarrollo de las instituciones federales de control externo, caracterizado por la alternancia entre períodos de expansión y de retracción de sus atribuciones. Para avanzar en el conocimiento acerca de este patrón histórico es necesario profundizar las investigaciones sobre el momento en el cual se establecieron las bases de su construcción, la Primera República. Este estudio pretende ser una contribución a la superación de esa laguna. Sostiene que el desarrollo de las instituciones federales de control externo en el período en cuestión se caracterizó por la expansión legal de atribuciones de 1890 a 1892, seguida de la abdicación práctica desde entonces hasta 1930, por drift institucional, de la responsabilidad de juzgar las cuentas anuales del gobierno. El estudio es institucionalista histórico y se compuso a partir del análisis de fuentes primarias.

Abstract This research deals with the development of the federal institutions of external control during the First Brazilian Republic. This subject is scarcely explored in the literature. In general, it is addressed as a background in studies focusing on the recent history of the Federal Court of Accounts, characterized by the emergence of the New Republic (started in 1985). Such studies suggest a historical pattern in the development of federal institutions of external control, characterized by the alternation between periods of expansion and retraction of their attributions. To advance the knowledge of this historical pattern and contribute to expanding the literature on these institutions, we need a more in-depth look at the period of they were established, i.e., the First Brazilian Republic. This study suggests that the development of federal external control institutions in the First Brazilian Republic was characterized by the legal expansion of attributions from 1890 to 1892, followed by the practical abdication until 1930 by the institutional drift of the responsibility of judging the annual accounts of the government. This is a historical institutionalist study based on the analysis of primary sources.

Correlated gamma frailty models for bivariate survival time data.

Frailty models have been developed to quantify both heterogeneity as well as association in multivariate time-to-event data. In recent years, numerous shared and correlated frailty models have been proposed in the survival literature allowing for different association structures and frailty distributions. A bivariate correlated gamma frailty model with an additive decomposition of the frailty variables into a sum of independent gamma components was introduced before. Although this model has a very convenient closed-form representation for the bivariate survival function, the correlation among event- or subject-specific frailties is bounded above which becomes a severe limitation when the values of the two frailty variances differ substantially. In this article, we review existing correlated gamma frailty models and propose novel ones based on bivariate gamma frailty distributions. Such models are found to be useful for the analysis of bivariate survival time data regardless of the censoring type involved. The frailty methodology was applied to right-censored and left-truncated Danish twins mortality data and serological survey current status data on varicella zoster virus and parvovirus B19 infections in Belgium. From our analyses, it has been shown that fitting more flexible correlated gamma frailty models in terms of the imposed association and correlation structure outperforms existing frailty models including the one with an additive decomposition.