Drivers and mechanisms of tree mortality in moist tropical forests

Tree mortality rates appear to be increasing in moist tropical forests (MTFs) with significant carbon cycle consequences. Here, we review the state of knowledge regarding MTF tree mortality, create a conceptual framework with testable hypotheses regarding the drivers, mechanisms and interactions that may underlie increasing MTF mortality rates, and identify the next steps for improved understanding and reduced prediction. Increasing mortality rates are associated with rising temperature and vapor pressure deficit, liana abundance, drought, wind events, fire and, possibly, CO2 fertilization-induced increases in stand thinning or acceleration of trees reaching larger, more vulnerable heights. The majority of these mortality drivers may kill trees in part through carbon starvation and hydraulic failure. The relative importance of each driver is unknown. High species diversity may buffer MTFs against large-scale mortality events, but recent and expected trends in mortality drivers give reason for concern regarding increasing mortality within MTFs. Models of tropical tree mortality are advancing the representation of hydraulics, carbon and demography, but require more empirical knowledge regarding the most common drivers and their subsequent mechanisms. We outline critical datasets and model developments required to test hypotheses regarding the underlying causes of increasing MTF mortality rates, and improve prediction of future mortality under climate change

Item response theory: sample size influence on the estimation of item parameters using Enem microdata

O presente estudo visa corroborar a disseminação dos conhecimentos acerca da Teoria da Resposta ao Item (TRI) em avaliações educacionais, em especial, no Exame Nacional do Ensino Médio (Enem), ao buscar verificar os impactos do tamanho da amostra na estimação dos parâmetros dos itens com base nos microdados do Enem de 2018. Para atingir tal objetivo, esse trabalho buscou conceituar o significado de avaliação educacional, tangenciou a metodologia numérica tradicional de quantificação dos resultados em testes (TCT Teoria Clássica dos Testes) e revisitou os embasamentos matemáticos e estatísticos da TRI. Com base em uma análise de documentos, buscou-se reconstruir o modo de aplicação da TRI pelo Instituto Nacional de Estudos e Pesquisas Educacionais Anísio Teixeira (INEP) nas aplicações do Enem. Além da apresentação e discussão dos resultados, o presente estudo disponibiliza integralmente o código desenvolvido, em linguagem R, para a construção de um painel web que permite a estimação de parâmetros dos itens e proficiência dos indivíduos pela TRI no modelo logístico de três parâmetros (ML3).The present study aims to corroborate the dissemination of knowledge about the Item Response Theory (IRT) in educational assessments, especially in the Exame Nacional do Ensino Médio (Enem), by seeking to verify the impacts of the sample size in the estimation of the parameters of the items based on the 2018 Enem microdata. To achieve this goal, this work sought to conceptualize the meaning of educational assessment, superficially passed on the traditional numerical methodology for quantifying test results (CTT - Classical Test Theory) and revisited the mathematical and statistical bases of IRT. Based on an analysis of documents, an attempt was made to reconstruct the way in which the IRT is applied by the Instituto Nacional de Estudos e Pesquisas Educacionais Anísio Teixeira (INEP) in Enem applications. In addition to the presentation and discussion of the results, the present study fully provides the code developed, in R language, for the construction of a web panel that allows the estimation of itens parameters and individuals proficiencies by TRI in the three-parameter logistic model (ML3)