Browsing by Author "Meza, Cristian"

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    Classification of longitudinal data through a semiparametric mixed-effects model based on lasso-type estimators
    (2015) Arribas-Gil, Ana; Cruz Mesía, Rolando J. de la; Lebarbier, Emilie; Meza, Cristian
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    Estimation in nonlinear mixed-effects models using heavy-tailed distributions
    (2012) Meza, Cristian; Osorio, Felipe; De la Cruz, Rolando
    Nonlinear mixed-effects models are very useful to analyze repeated measures data and are used in a variety of applications. Normal distributions for random effects and residual errors are usually assumed, but such assumptions make inferences vulnerable to the presence of outliers. In this work, we introduce an extension of a normal nonlinear mixed-effects model considering a subclass of elliptical contoured distributions for both random effects and residual errors. This elliptical subclass, the scale mixtures of normal (SMN) distributions, includes heavy-tailed multivariate distributions, such as Student-t, the contaminated normal and slash, among others, and represents an interesting alternative to outliers accommodation maintaining the elegance and simplicity of the maximum likelihood theory. We propose an exact estimation procedure to obtain the maximum likelihood estimates of the fixed-effects and variance components, using a stochastic approximation of the EM algorithm. We compare the performance of the normal and the SMN models with two real data sets.
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    New insights from GWAS on BMI-related growth traits in a longitudinal cohort of admixed children with Native American and European ancestry
    (CELL PRESS, 2023) Vicuña, Lucas; Barrientos, Esteban; Norambuena, Tomás; Alvares, Danilo; Gana Ansaldo, Juan Cristóbal; Leiva Yamaguchi, Valeria; Meza, Cristian; Lorenzoni Santos, José Guillermo; Mericq, Verónica; Pereira, Ana; Eyheramendy, Susana
    Body-mass index (BMI) is a hallmark of adiposity. In contrast with adulthood, the genetic architecture of BMI during childhood is poorly understood. The few genome-wide association studies (GWAS) on children have been performed almost exclusively in Europeans and at single ages. We performed cross-sectional and longitudinal GWAS for BMI-related traits on 904 admixed children with mostly Mapuche Native American and European ancestries. We found regulatory variants of the immune gene HLA-DQB3 strongly associated with BMI at 1.5 - 2.5 years old. A variant in the sex-determining gene DMRT1 was associated with the age at adiposity rebound (Age-AR) in girls (P = 9.8 x 10(-9)). BMI was significantly higher in Mapuche than in Europeans between 5.5 and 16.5 years old. Finally, Age-AR was significantly lower (P = 0.004) by 1.94 years and BMI at AR was significantly higher (P = 0.04) by 1.2 kg/m(2), in Mapuche children compared with Europeans.
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    Performance of port facilities in southern Chile during the 27 february 2010 Maule Earthquake
    (SAGE PUBLICATIONS INC, 2012) Brunet Gutiérrez, Santiago José; Llera Martin, Juan Carlos de la; Jacobsen Pohlenz, Andrés; Miranda, Eduardo; Meza, Cristian
    This article describes the seismic performance of a group of ports in southern Chile during the 27 February 2010 Maule, Chile, earthquake. Direct costs in damage for these ports have been estimated in slightly less than US$300 million. Similarly to the performance of other ports in previous earthquakes, the most common failures observed were soil related, and include soil liquefaction, lateral spreading, and pile failures. Structural failures were mostly due to short pile effects and natural torsion. This situation is contrasted herein with the performance of the South Coronel Pier, which was seismically isolated in 2007. The isolated portion of this port remained operational after the earthquake, which was the main design goal. Post-earthquake preliminary analyses indicate that the structure was subjected to deformations and forces of approximately 60% to 70% of their design values, respectively. Piles and superstructure remained within elastic range, while the isolators experienced important nonlinear deformations. [DOI: 10.1193/1.4000022]