[R] poLCA

Lucy lucygallienne at gmail.com
Thu Mar 8 23:02:38 CET 2012

I am running some latent class models with civariates using poLCA in R, and 
have a question the meaning of some error messages.

My model has 8 y-variables (dichotomous) and 2 x-variables (also dichotomous),
and I am trialling different numbers of classes.

When I run a 2-class model, the model runs fine without any error messages. I 
used the nrep = 10 option to avoid local maxima. Class % are ~81% and 19%.

When I trial a 3-class model,  firstly I upped the nrep to 200, since for some 
runs it isn't till run 139 that the maximum is found. Class % are ~81%, 16% 
and 2%. These vary a LOT if a model based on a local maximum is used.
Anyway, for the final model with max, I get the following message:

Warning messages:
1: In sqrt(diag(VCE.beta)) : NaNs produced
2: In sqrt(diag(VCE.beta)) : NaNs produced
3: In sqrt(diag(VCE.mix)) : NaNs produced
4: In sqrt(diag(VCE.beta)) : NaNs produced
5: In sqrt(diag(VCE.mix)) : NaNs produced

What does this mean for the model?

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