how to know if random factors are significant?

Dear all:
Thank you very much all for your comments. I?m trying everything you said and checked 
previous messages from Marianne, John and Douglas Bates. I found that removing the 
random factor reduced the p-values for fixed effects (as John mentioned) and this new 
model has not better significant power indicated by the likelihood ration test. 
So, even with a low Variance the random factor must be used in a mix model effects.

Thank you very much for your help. I'm understanding and learning so much with the "R-
help lists".

Leo

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