Activities (y in my model) is measured by time doing certain activity. I have many "0" time observation in my file, then I'm trying to analyze with GLINMIX using Poisson distribution.
Time involved in a certain activity doesn't seem like a Poisson distribution to me.
But probably the reason you are getting least squares means less than zero is that you are not using the ILINK option in the LSMEANS statement which should invert the log transformation and then no value can be less than zero.
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