[R-sig-ME] poisson GLMER with identity link

Tim Carnus tim.carnus at gmail.com
Thu Apr 1 20:12:55 CEST 2010

Dear list,

Just adding an example of the model I am fitting, and session info.


where I am interested in the additive effects of X1-X4 on the count per
plot response. The random effect is simply there to account for the
repeated measures taken over time on each plot.

R version 2.10.1 (2009-12-14) 

On Mon, 2010-03-29 at 17:45 +0100, Tim Carnus wrote:
> Dear list,
> I am trying to fit a number of GLMERs to count data with an additive
> model (in the predictors) that requires the use of the identity link
> function. For about half of my response variables this causes no
> problems. However in a number of cases the model fitting runs into
> problems with regards estimation of negative mean (for e.g. the error
> message in mer_finalize: mu[i] must be positive: mu = 1.76267e-312, i =
> 13075456). As far as I understand this is well known and documented, and
> guarding against that possibility is necessary, and built in to say the
> glm() function.
> My question then is, how can I do this with lmer? (ie how can I specify
> the constraints necessary to fit these types of models, if at all
> possible)
> Best regards,
> Tim Carnus
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