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Tuyển tập các báo cáo nghiên cứu về sinh học được đăng trên tạp chí sinh học thế giới đề tài: Attenuating effects of preferential treatment with Student-t mixed linear models: a simulation study | Genet. Sei. Evol. 30 1998 565-583 @ Inra Elsevier Paris 565 Original article Attenuating effects of preferential treatment with Student-t mixed linear models a simulation study Ismo Strandéna b Daniel Gianolaa a Department of Animal Sciences University of Wisconsin Madison WI 53706 USA b Animal Production Research Agricultural Research Centre - MTT 31600 Jokioinen Finland Received 14 May 1998 accepted 16 October 1998 Abstract Preferential treatment of cows in four herds of a multiple ovulation and embryo transfer scheme under selection was simulated. Prevalence and amount of preferential treatment depended on a function correlated with true breeding value. Three mixed effect linear models were compared in terms of their ability to handle preferential treatment the classical Gaussian model a model with multivariate t-distributed errors clustered by herd and a model with independent t-distributed errors. In the models with t-distributed errors both the scale parameters and the degrees of freedom were considered unknown. A Bayesian analysis was carried out for all three models via the Gibbs sampler and posterior means were used to infer about genetic variance herd-year effects breeding values and realised response to selection. Performance over repeated sampling was assessed via Monte Carlo mean squared error. In the absence of preferential treatment the three models had a similar performance. When preferential treatment was prevalent and strong the univariate t-model was the best hence the Gaussian assumption for the errors was clearly inappropriate. It appears that some robust linear models can handle preferential treatment of animals better than the standard mixed effect linear model with Gaussian assumptions. Inra Elsevier Paris dairy cattle preferential treatment simulation Bayesian statistics Student-t distribution I Gibbs sampling Resume Attenuation des effets de traitement preferentiel dans un modèle linéaire mixte à distribution de student t . Etude de .
