Assessment of heterogeneity of residual variances using changepoint techniques

Genetics Selection Evolution

Miguel A Toro¹  Maria J Carabaño¹  Romdhane Rekaya² 

[1] Area de Mejora Genética Animal, CIT-INIA, Carretera de la Coruna Km 7, 28040 Madrid, Spain;Department of Dairy Science, University of Wisconsin, Madison 53706, USA

关键词: residual variance;    heterogeneity;    changepoint;   

Others  :  1094791
DOI  :  10.1186/1297-9686-32-4-383

 received in 2000-01-25, accepted in 2000-04-25,  发布年份 2000

【 摘 要 】

Several studies using test-day models show clear heterogeneity of residual variance along lactation. A changepoint technique to account for this heterogeneity is proposed. The data set included 100 744 test-day records of 10 869 Holstein-Friesian cows from northern Spain. A three-stage hierarchical model using the Wood lactation function was employed. Two unknown changepoints at times T₁ and T₂, (0 <T₁ <T₂ <t_max), with continuity of residual variance at these points, were assumed. Also, a nonlinear relationship between residual variance and the number of days of milking t was postulated. The residual variance at a time t() in the lactation phase i was modeled as: for (i = 1, 2, 3), where λ_ι is a phase-specific parameter. A Bayesian analysis using Gibbs sampling and the Metropolis-Hastings algorithm for marginalization was implemented. After a burn-in of 20 000 iterations, 40 000 samples were drawn to estimate posterior features. The posterior modes of T₁, T₂, λ₁, λ₂, λ₃, , , were 53.2 and 248.2 days; 0.575, -0.406, 0.797 and 0.702, 34.63 and 0.0455 kg², respectively. The residual variance predicted using these point estimates were 2.64, 6.88, 3.59 and 4.35 kg² at days of milking 10, 53, 248 and 305, respectively. This technique requires less restrictive assumptions and the model has fewer parameters than other methods proposed to account for the heterogeneity of residual variance during lactation.

【 授权许可】

   
2000 INRA, EDP Sciences