[R] [EXT] Predicted values from glm() when linear predictor is NA.

Rolf Turner r@turner @end|ng |rom @uck|@nd@@c@nz
Thu Jul 28 03:58:44 CEST 2022

On Thu, 28 Jul 2022 00:41:52 +0000
Andrew Robinson <apro using unimelb.edu.au> wrote:

> Hi Rolf,
> that's an interesting observation.
> I agree that it is counter-intuitive that the fitted values /
> predictions are not NA.

That gives me some comfort!

Does anyone from R-core feel like commenting?

> However, I don't agree with your comment that <<if the linear
> predictor in a Binomial glm is NA, then "success" is a certainty>> -
> that seems to be a peculiarity of these data - note for these three
> observations there are thousands dead and zero alive and that you get
> similar outcomes if you omit TrtTime altogether ...
> > predict(glm(cbind(Dead,Alive) ~ Lifestage,
> > family=binomial,data=demoDat))[demoDat$Lifestage=="L1"]
>  26 65 131
> 20.02007 20.02007 20.02007

Hmm.  Yeah.  I was probably jumping the gun a bit there.  I'll think on
this a bit more.

This issue arose in a more complicated context (which I won't try to go
into) in which I really need some insight into how to deal with missing
values of the linear predictor, and what the resulting fitted values
actually mean.  Psigh!



Honorary Research Fellow
Department of Statistics
University of Auckland
Phone: +64-9-373-7599 ext. 88276

More information about the R-help mailing list