Tuyển tập các báo cáo nghiên cứu về sinh học được đăng trên tạp chí sinh học thế giới đề tài: A comparison between Poisson and zero-inflated Poisson regression models with an application to number of black spots in Corriedale sheep | Genet. Sel. Evol. 40 2008 379-394 INRA EDP Sciences 2008 DOI gse 2008010 Available online at Original article A comparison between Poisson and zero-inflated Poisson regression models with an application to number of black spots in Corriedale sheep Hugo Naya1 2 3 Jorge I. Urioste2 Yu-Mei Chang3 Mariana Rodrigues-Motta3 Roberto Kremer4 Daniel Gianola3 1Unidad de Bioinformatica Institut Pasteur de Montevideo Mataojo 2020 Montevideo 11400 Uruguay 2Departamento de Produccion Animal y Pasturas Facultad de Agronomia Av. Garzon 780 Montevideo 12900 Uruguay 3Department of Animal Sciences University of Wisconsin-Madison Madison WI 53706 UsA 4Departamento de Ovinos y Lanas Facultad de Veterinaria Av. Lasplaces 1550 Montevideo 11600 Uruguay Received 15 October 2007 accepted 16 January 2008 Abstract - Dark spots in the fleece area are often associated with dark fibres in wool which limits its competitiveness with other textile fibres. Field data from a sheep experiment in Uruguay revealed an excess number of zeros for dark spots. We compared the performance of four Poisson and zero-inflated Poisson ZIP models under four simulation scenarios. All models performed reasonably well under the same scenario for which the data were simulated. The deviance information criterion favoured a Poisson model with residual while the ZIP model with a residual gave estimates closer to their true values under all simulation scenarios. Both Poisson and ZIP models with an error term at the regression level performed better than their counterparts without such an error. Field data from Corriedale sheep were analysed with Poisson and ZIP models with residuals. Parameter estimates were similar for both models. Although the posterior distribution of the sire variance was skewed due to a small number of rams in the dataset the median of this variance suggested a scope for genetic selection. The main environmental factor was the age of the sheep at shearing. In summary age .
