[R] add1 GLM - Warning message, what does it mean?

[Prof Brian Ripley]

On Thu, 19 Jan 2012, Jhope wrote:

> Hi All, I am wondering if anyone can tell me what the warning message below
> the model means?

Which one?: there are two warnings!

1) most likely indicates that Rayos is a character variable.

2) indicates that you have missing values in the variables you are 
trying to add, and so the fits were done on the cases which are 
complete for all the variables included and the AICs are not 
comparable.

Had we had the 'commented, minimal, self-contained, reproducible code' 
we asked you for, this would have been much clearer.

>
> J
>
> add1(DTA.glm,~ Aeventexhumed + Veg + Berm + HTL + Estuary + Rayos)
> Single term additions
>
> Model:
> cbind(MaxHatch, TotalEggs - MaxHatch) ~ Aeventexhumed + Veg +
>    Berm + HTL
>        Df Deviance    AIC
> <none>       488.86 4232.9
> Estuary  1   454.96 4201.0
> Rayos    3   258.80 4008.9
> Warning messages:
> 1: In model.matrix.default(Terms, m, contrasts.arg = object$contrasts) :
>  variable 'Rayos' converted to a factor
> 2: In add1.glm(DTA.glm, ~Aeventexhumed + Veg + Berm + HTL + Estuary +  :
>  using the 17/83 rows from a combined fit
>
> --
> View this message in context: http://r.789695.n4.nabble.com/add1-GLM-Warning-message-what-does-it-mean-tp4309553p4309553.html
> Sent from the R help mailing list archive at Nabble.com.
>
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>

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595