[R] nested random factor using lme produces errors

melswed amelie.truchy at slu.se
Sun Feb 17 16:56:02 CET 2013


I am running a mixed-effect model with a nested-random effect. I am
interested in gut parasites in moose. I has three different type of
treatment that I applied to moose which are from different "families". My
response variable is gut parasites and the factors are moose families which
is nested within treatment. My data is balanced.

To answer this question, I used the lme function like this :

But doing a summary on this model gives me warning message :
In pt(-abs(tTable[, "t-value"]), tTable[, "DF"]) : NaNs produced

I don't understand why ?! I noticed that the p-values are not computed and
have NAs values for drug2 and drug3 (from the summary of this model)

Moreover, in the summary, I noticed that in the random effects line I have
standard deviation for Formula: ~1 | drug and for Formula: ~1 | family %in%
drug. Does R consider drug as a random factor as well ?

And last question, how can I know if my random factor has a significant
effect on the gut parasites ?

Thank for your help,

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