RE: ASREML GLMM with animal model
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RE: ASREML GLMM with animal model

Dear ASREML'ers
	I have some experience in using ASREML GLMM for binomial data 
sets. In one set of ASREML analysis on dairy cattle data on diseases 
(>70000 records, incidence range 2-15%), I compared genetic 
parameters of 6 binomial disease traits from univariate-threshold animal 
model, threshold 'sire' model (both are GLMM with probit link) and linear 
animal model (GLMM without any link functions). Results were different 
for animal versus sire (threshold) models. I kept linear model as a base 
to which threshold model estimates were compared (after some 
transformation to 0/1 scale). Only results from sire model seemed 
"plausible" and animal model estimates went wild especially at extreme 
	We concluded that sire models are more appropriate to use 
i) threshold models are based on Taylor series expansion and/or
ii) the animal model works at individual level where as sire model works 
in progeny groups, where the later benefit from central limit theorem that 
has much impact in terms of progeny group size and incidence.
iii) the fact that threshold models are still sensitive to incidences (as 
Arthur also noted), suggests that threshold models are not independant 
of the mean which is bit worrying.
	Obviously these problems are global and so we would expect this 
to happen with any type of software designed to do the job.
		I think most of this is in line with those of Arthur and Luc. 

Dr. Haja Kadarmideen
Animal Breeding and Genetics Department
Animal Biology Division
Scottish Agricultural College (Edinburgh)  
Bush Estates
Penicuik, Midlothian EH26 0PH
Scotland, UK

Telephone: +44 0131 535 3246
Fax      : +44 0131 535 3121 

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