# Re: why use pi^2/3 replace of error variance 1 in binomial analysis?

From: I.M.S.White <i.m.s.white_at_ED.AC.UK>
Date: Tue, 31 Mar 2009 10:24:13 +0100

One way the probit and logit links arise is when the event in question is
triggered by an unobserved variable exceeding a fixed threshold. Fixed
effects and variances are measured on this underlying (threshold,
liability) scale. If we assume the unobserved threshold variable is
standard normal (with variance one) we get the probit link, and if we
assume a standard logistic
distribution (which has a variance of pi^2/3) we get the logit link.

Quoting luansheng <luansheng_at_GMAIL.COM>:

> In the p333 of asreml 3 user guide, it is about an analysis of footrot as a
> binomial variable using the logistic link. In this example, using pi^2/3
> replace of error variance 1. I don't know the reason, anyone tell me?
> thanks!
>
> --
> Luan sheng
> ----------------------------------------
> Yellow Sea Fisheries Research Institute
> Chinese Academy of Fisheries Sciences
> Nanjing Road 106
> Qingdao 266071
> China
> luansheng_at_gmail.com
> luansheng_at_ysfri.ac.cn
> ----------------------------------------
>
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Received on Wed Mar 31 2009 - 10:24:13 EST

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