Dear Douglas,

thank you very much for your message. If necessary I can send you my data
set. Before let me show you the output of the verbose=TRUE and the summary
of the model results (see below).
I wonder wether the problem is that the variance estimated for the main
random effect (study area: coded as 'ter') takes the value of 0 (third
column in the results of the 'verbose'). If that would be the problem, I
wonder whether it would be acceptable (dessing) that I would ommit this
random effect in the models and only considering the random effect of the
transects (coded as 'trans'). On the other hand, I don't understand why
this problem only happens with some of the independent variables (other
models fitted fine).
Thank you very much in advance,

Toni

mod05<-lmer(cagaders~E_arb_alt+(1|ter)+(1|ter:trans),data=conill,family=poisson,verbose=TRUE)

 0:     1580.1040: 0.521157 0.212762 0.0146621 -0.00550703
 1:     1578.7769: 0.529048 0.217137 0.0121796 -0.00198275
 2:     1574.8963: 0.536915 0.221586 0.00963723 -0.00542672
 3:     1546.2308: 0.659172 0.290027 -0.0296622 -2.71216e-05
 4:     1544.4481: 0.659755 0.290395 -0.0299398 -0.00438446
 5:     1512.2918: 0.827224 0.356975 -0.453220 0.000576404
 6:     1506.1926:  1.14082 0.0210690 -0.431339 -0.00365397
 7:     1500.5942:  1.16992  0.00000 -0.828777 0.00123612
 8:     1500.3060:  1.20528  0.00000 -0.790690 0.00198426
 9:     1499.5992:  1.25168  0.00000 -0.779210 0.000659413
10:     1499.3691:  1.28723  0.00000 -0.803391 0.000445819
11:     1499.2722:  1.32511  0.00000 -0.837827 0.000455882
12:     1499.2705:  1.33004  0.00000 -0.843619 0.000496015
13:     1499.2704:  1.33032  0.00000 -0.844199 0.000502862
14:     1499.2704:  1.33030  0.00000 -0.844231 0.000503448
Mensajes de aviso perdidos
In mer_finalize(ans) : singular convergence (7)



SUMMARY
Generalized linear mixed model fit by the Laplace approximation Formula:
cagaders ~ E_arb_alt + (1 | ter) + (1 | ter:trans)   Data: conill  AIC  BIC
logLik deviance
1507 1525 -749.6     1499
Random effects:
Groups    Name        Variance Std.Dev.
ter:trans (Intercept) 1.7697   1.3303  ter       (Intercept) 0.0000
0.0000  Number of obs: 648, groups: ter:trans, 66; ter, 11

Fixed effects:
            Estimate Std. Error z value Pr(>|z|)    (Intercept) -0.8442310
0.1839531  -4.589 4.45e-06 ***
E_arb_alt    0.0005023  0.0029302   0.171    0.864    ---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
Correlation of Fixed Effects:
        (Intr)
E_arb_alt -0.247





On Thu, Feb 9, 2012 at 9:03 PM, Douglas Bates <bates@stat.wisc.edu> wrote:

> On Thu, Feb 9, 2012 at 11:08 AM, Toni Hernandez-Matias
> <ahmatias@gmail.com> wrote:
> > Dear all,
>
> > I am trying to fit a set of models with lmer function.
> > My aim is to investigate the relationship between the abundance of a
> mammal
> > species (count) and several environmental variables.
> > The sample size is 648, but the observations are not independent and the
> > random effect is nested: I have 10 study areas, within each area I
> > performed 6 transects. I have 9-10 observations in all transects. So an
> > example of a model with a single independent variable is:
> >
> mod05<-lmer(cagaders~E_arb_alt+(1|ter)+(1|ter:trans),data=conill,family=poisson)
>
> > When running this model I get the warning:
> > In mer_finalize(ans) : singular convergence (7)
>
> Try using verbose=TRUE to determine where the parameter values are
> going during the iterative optimization process.
>
> If your data could be made available, even in an anonymized form, we
> could check the model fit against other optimizers that may be more
> successful.
>
> > I don't see an apparent reason for this warning.
> > I would be very grateful if someone can help me to solve this problem and
> > to know wether the results in the fitted model are credible.
> >
> > Thank you very much in advance,
> >
> > Toni
> >
>

-- 
*********************************************************

Antonio Hernandez Matias

Departament de Biologia Animal (Vertebrats)
Facultat de Biologia
Universitat de Barcelona
Av. Diagonal, 645
Barcelona      08028
Spain
Telephone: +34-934035857
FAX: +34-934035740
e-mail: ahernandezmatias@ub.edu

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