From jfox at mcmaster.ca  Tue Jan 20 14:31:08 2004
From: jfox at mcmaster.ca (John Fox)
Date: Tue Jan 20 14:27:03 2004
Subject: [Rd] rstandard.glm() in base/R/lm.influence.R
In-Reply-To: <Pine.LNX.4.44.0401201408060.12918-100000@reclus.nhh.no>
Message-ID: <5.1.0.14.2.20040120082940.0203ef98@127.0.0.1>

By the way, it looks to me like Roger is right.

John

At 02:16 PM 1/20/2004 +0100, Roger Bivand wrote:
>I contacted John Fox about this first, because parts of the file are
>attributed to him. He says that he didn't write rstandard.glm(), and
>suggests asking r-devel.
>
>As it stands, rstandard.glm() has summary(model)$dispersion outside the
>sqrt(), while in rstandard.lm(), the sd is already sqrt()ed. This seems to
>follow stdres()  in VR/MASS/R/stdres.R.
>
>Of course for the c("poisson", "binomial")  families,
>summary(model)$dispersion is 1, so sqrt doesn't make a difference, but
>working with an epidemiologist, Marilia Carvalho, we wanted to map the
>standardised residuals of a quasipoisson null model of cases offset by
>log(pop.at.risk), and rstandard.glm() seemed to compress the values more
>than we'd have expected. Her colleague: "Valeska (L.  Andreozzi) says that
>she has already noticed that, and as McCullagh & Nelder (2nd ed, pg 397)
>says, the dispersion is inside the sqrt". (That's the way I read 12.5 on
>p. 397 too). I can't see that summary(model)$dispersion has already been
>subject to sqrt() in sum(object$weights * object$residuals^2)/df.r in
>summary.glm().
>
>Should:
>
>     res / (summary(model)$dispersion * sqrt(1 - infl$hat))
>
>be:
>
>     res / (sqrt(summary(model)$dispersion * (1 - infl$hat)))
>
>on line 117 in base/R/lm.influence.R?
>
>Best wishes,
>
>Roger
>
>--
>Roger Bivand
>Econonic Geography Section, Department of Economics, Norwegian School of
>Economics and Business Administration, Breiviksveien 40, N-5045 Bergen,
>Norway, voice: +47-55959355, fax: +47-55959393; Roger.Bivand@nhh.no
>
>______________________________________________
>R-devel@stat.math.ethz.ch mailing list
>https://www.stat.math.ethz.ch/mailman/listinfo/r-devel

-----------------------------------------------------
John Fox
Department of Sociology
McMaster University
Hamilton, Ontario, Canada L8S 4M4
email: jfox@mcmaster.ca
phone: 905-525-9140x23604
web: www.socsci.mcmaster.ca/jfox


[Rd] rstandard.glm() in base/R/lm.influence.R
John Fox