[R-sig-ME] false convergence (8) with binary covariate (0, 1) but NOT if covariate is (no, yes)?

[Paul Metzner]

> a) Why is that so?


Is it possible that you coded the variable as an integer before and as a factor now?  I'm not sure if lmer treats a two-level integer as a factor, but that might have been it.

> b) How can I fix the false convergence problem if my covariate has also a binary format?

You might try to apply sum contrasts, i.e., -1/2 and 1/2.  Everybody please correct me if this is nonsense.

Best,
Paul


On 8 Mar 2011, at 14:25, Julia Sommerfeld wrote:

> Dear list,
> 
> The false convergence warning message (8) seems to be a common problem in
> lmer. I've searched the archives to find a solution and found out that one
> approach would be standardizing my covariate to mean-center the data.
> 
> However, what if the covariate itself (in this case SameMate) has a binary
> value (0,1)?
> 
> After testing for the effect of the breeding success on site-fidelity (and
> finally understanding the summary output), I would like to account for the
> effect of breeding success (successfull=1, unsuccessfull=0) on mate-fidelity
> (mate-fidelity=1, no mate-fidelity=0).
> 
> I.e. does the model including BreedSuc1 fits better than without it:
> 
> fm<-lmer(SameMate~BreedSuc1+(1|Bird),family="binomial")
> fm1<-lmer(SameMate~1+(1|Bird),family="binomial")
> 
> Both models get the warning message:
> 
> In mer_finalize(ans) : false convergence (8)
> 
> anova(fm,fm1)
> Data:
> Models:
> fm1: SameMate ~ 1 + (1 | Bird)
> fm:   SameMate ~ BreedSuc1 + (1 | Bird)
>       Df    AIC      BIC        logLik   Chisq  Chi Df   Pr(>Chisq)
> fm1  2    48.659  52.946  -22.330
> fm    3    50.342  56.771  -22.171 0.3174      1     0.5732
> 
> Now the weird thing:
> 
> I simply changed the coding of my covariate from "0,1" to "no, yes". Now,
> only model fm1 gets the false convergence message:
> 
>> fm<-lmer(SameMate~BreedSuc1+(1|Bird),family="binomial")
>> fm1<-lmer(SameMate~1+(1|Bird),family="binomial")
> Warning message:
> In mer_finalize(ans) : false convergence (8)
> 
> Data:
> Models:
> fm1: SameMate ~ 1 + (1 | Bird)
> fm:   SameMate ~ BreedSuc1 + (1 | Bird)
>         Df    AIC     BIC        logLik       Chisq Chi Df
> Pr(>Chisq)
> fm1   2     47.490 51.468   -21.745
> fm     3     54.096 60.063    -24.048     0             1          1
> 
> a) Why is that so?
> b) How can I fix the false convergence problem if my covariate has also a
> binary format?
> 
> I would highly appreciate suggestions and ideas.
> 
> Cheers,
> 
> Julia
> 
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