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*To*: wilsonvl@grove.ufl.edu*Subject*: Re: Binomial data*From*: gilmoua@ornsun.agric.nsw.gov.au (Arthur Gilmour)*Date*: Tue, 16 Dec 1997 15:35:35 +1100*Cc*: asreml@chiswick.anprod.CSIRO.AU*Sender*: owner-asreml

> > 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. Arthur > > Uilson Lopes > > >

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