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poLCA

lucy
Hi,
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?
Cheers,
Lucy

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Re: poLCA

lucy
I understand that the NaN's mean that something can't be computed, I'm just unsure as to what they refer to. Can anyone shed some light as to what the beta and mix matrices are?