[R-sig-ME] Additive versus multiplicative overdispersion modeling

[David Duffy]

On Fri, 20 Aug 2010, Ned Dochtermann wrote:

> Thanks a lot, if that is indeed the case it makes calculating
> repeatabilities per N&S quite straightforward for the multiplicative
> models (quasibinomial & quasipoisson) since the relevant term to
> include in the denominator would just be (summary(model)@sigma)^2
> (multiplied by (pi^2)/3 ). Of course I still can't figure out how to
> get the needed information from the additive models, i.e. the residual
> of the distribution specific variance.
>

Method "C" in the Browne paper uses: r = V/(V+pi^2/3) for the logistic 
link, and r=V/(V+1) for the probit link (the latter is the tetrachoric r).

Cheers, David Duffy.

-- 
| David Duffy (MBBS PhD)                                         ,-_|\
| email: davidD at qimr.edu.au  ph: INT+61+7+3362-0217 fax: -0101  /     *
| Epidemiology Unit, Queensland Institute of Medical Research   \_,-._/
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