SE's for boundary fixed parameters
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SE's for boundary fixed parameters

Hi all,

In several analyses fitting both additive and permanent environmental
effects for animal (repeated records) ASREML has fixed one parameter
(usually additive) to the boundary. I knew this might happen with my data
as I do not have much pedigree depth or number of animals, but plenty of
repeated records. For highly heritable traits fitting both effects was
significantly better than either fitting one or the other, and the two
parameters were successfully separated (according to LRT etc). The
'boundary' traits have the same pedigree and design structure as traits
which converged normally, so there is obviously enough information in the
data (at least for highly heritable traits), but I suspect that the
'boundary' traits are not heritable at all.

So, my questions are:

1) does fixation of a particular parameter to the zero boundary indeed
reflect that this trait is not heritable? Following on from this, can it be
truly taken as evidence that the sole source of repeatability is the
permanent environment of the dam? This is in light of the fact that I know
estimates were obtained for both h2 and c2 for different traits under an
identical design structure.

2) are the standard errors truly representative for the parameter which was
sucessfully estimated? I know fixation can bias the remaining parameter
estimates (although this was not the case for my data) and would assume the
same might happen to SE's?

Thanks for your help


Kim Bunter (M.Rur.Sc)
PhD Student
Animal Genetics and Breeding Unit
University of New England
Armidale, NSW, 2351

Ph:  (02) 6773 3788
Fax: (02) 6773 3266
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