R help - Apr 2007 - Why warnings using lmer-model with family=binomial

Hi all!

My question is why, and what I can do about that 
I sometimes, but not always, get warning-messages like

nlminb returned message singular convergence (7)
  in: LMEopt(x = mer, value = cv)

or

IRLS iterations for PQL did not converge

when trying to fit a model looking like this: 
lmer<-(cbind(Diseased,Healthy)~Fungus+(1|Family)+(1|Fungus:Family), 
family="binomial") to four similar data sets?

All four data sets consists of four columns; 
Fungus (1 or 2), Family (1-30), Diseased and Healthy.
An example:

Fungus  Family          Diseased        Healthy
1               1               3               7
2               1               1               5
1               2               2               16
2               2               2               14

...and so on up to totally 30 families.

One of the data sets works perfectly fine and 
gives no warnings, but for the others i get 
different amount of warning messages. Between the 
data sets it is only the number of diseased anf 
healthy for each family and fungus that differ.
Does anyone have any idea why this happens and 
how I can get around it (I'm mainly interested in the interaction term...)?

Grateful for any help


/?sa

__________________________________________________________________

?sa Granberg, Doktorand / Phd-student

Evolution?r ekologi
Ekologi, milj? och geovetenskap
Ume? Universitet
901 87 Ume?

Evolutionary ecology
Department of Ecology and Environmental Science
Ume? University
901 87 Ume?, Sweden

Phone: +46 (0)90 786 7461
Fax: +46 (0)90 786 6705
e-mail:asa.granberg at emg.umu.se

On 4/11/07, ?sa Granberg <asa.granberg at emg.umu.se>
wrote:
> Hi all!
>
> My question is why, and what I can do about that
> I sometimes, but not always, get warning-messages like
>
> nlminb returned message singular convergence (7)
>   in: LMEopt(x = mer, value = cv)
>
> or
>
> IRLS iterations for PQL did not converge
>
> when trying to fit a model looking like this:
> lmer<-(cbind(Diseased,Healthy)~Fungus+(1|Family)+(1|Fungus:Family),
> family="binomial") to four similar data sets?
>
> All four data sets consists of four columns;
> Fungus (1 or 2), Family (1-30), Diseased and Healthy.
> An example:
>
> Fungus  Family          Diseased        Healthy
> 1               1               3               7
> 2               1               1               5
> 1               2               2               16
> 2               2               2               14
>
> ...and so on up to totally 30 families.
>
> One of the data sets works perfectly fine and
> gives no warnings, but for the others i get
> different amount of warning messages. Between the
> data sets it is only the number of diseased anf
> healthy for each family and fungus that differ.
> Does anyone have any idea why this happens and
> how I can get around it (I'm mainly interested in the interaction
term...)?
Do you have the latest released version of the lme4 package (version
0.9975-13) installed? You can check with

library(lme4)
sessionInfo()

My memory may be failing me but I thought that I changed the default
estimation method for generalized linear mixed models to minimization
of the Laplace approximation to the deviance before that release, in
which case no PQL iterations are being performed.

In any case it is recommended that you include the output from
sessionInfo() in messages dealing with specific behavior of R or R
packages.