> I am running some analysis with binary data in trees, using 0/1 data
> directly (not proportion or percent) and probit as link function
> (model: x !bin !probit !wt=0 ~ mu !r fam)
> Problem 1: I am confuse with the interpretation of variance components.
> Source Model terms Gamma Component Compnt/StndErr
> fam 80 80 0.165261 0.165261 4.39
> Variance 1920 1919 1.00000 1.00000 0.00
> I understand the variance components are expressed on underlying scale
> (threshold model). In the example above the family variance component is
> 0.165261. But what about the error variance component? Is it just 1-
> 0.165261=0.834739? If this is true, then, ASREML just sets the phenotypic
> variance to 1 without estimation of the other portion of the variance. Is
> that right?
The model is probit(x) = mu + random(fam) + error.
The probit transformation is based on the standard Normal distribution
which has a variance of 1. Therefore the error variance
on the underlying scale is 1. The family variance is .165
So the phenotypic variance is 1.165
heritability is C times .165 / 1.165 where C is 4 for halfsib
families but often taken as 2.5 in trees.
> Problem 2: When dealing with binomial data, does Asreml use the methods
> described in Gilmour et al 1985 (The analysis of binomial data by a
> generalized linear mixed model)? Or other methods are used?
This is not the method of Gilmour et al 1985
Rather, it is the method of Schall Biometrika 78 719-727 (1991)
> Thank you very much all of you.
> Have a happy new year.
I also wish you all a very happy time over christmas and new year.
I'll be having a fortnight off.
Thank you all for friendship and encouragement and patient understanding.
> Uilson Lopes