[R] lme4 and false convergence

From: Ben Zuckerberg <bz73_at_cornell.edu>
Date: Mon, 24 Nov 2008 12:37:09 -0500

Dear R-users,

I am using the most updated package of lme4 (lme4_0.999375-2). I have a data set consisting of ~900 observations at ~440 independent survey sites. There are an unbalanced number of surveys at each site. I am attempting to develop several models evaluating the presence/absence of a species (PRES) at these random sites (SITE) using a number of predictor variables. The response variable (PRES) is binomial and the included predictor variables are either proportions (e.g., AG, FOR, OPEN, LDEV,or DEV) or numerical (COUNT[min. 1 to max. 37,mean = 10]).

PROBLEM 1:   I have developed the following GLMM:  


I receive the following error:
Warning message:
In mer_finalize(ans) : false convergence (8)  

There is model output, but I am worried it might be biased.  

I have tried:
-Data transformation of the predictor variables (e.g., log(COUNT)),
which does seem successful in some simpler models, but does not work consistently.
-The most updated version of lme4

In addition, I am interested in visualizing the predicted probabilities from this output using the fixed effect function, but receive the following message:  

Error in UseMethod("fixef") : no applicable method for "fixef"  

Any suggestions would be greatly appreciated!

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