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Using anova vs. Anova for linear mixed model

1 message · John Fox

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John Fox
# 
Dear Kevin,

It's not entirely clear to me what you did, because as far as I know, the anova() method for merMod objects supplied by the lme4 package doesn't have a type argument and computes sequential ("type-I") tests. (You say that you're using anova() in the stats package, but while stats provides the anova() generic function, the method is coming from someplace else.)

That said, I suspect that the discrepancy is due to the empty cells in the table of the fixed-effects factors. Normally, Anova() will detect the resulting aliased coefficients in the model and report an error, but I believe that lmer() suppresses the aliased coefficients by removing redundant columns of the model matrix. Whatever anova() method you used apparently detected the empty cells directly and printed a warning.

Finally, and particularly in light of the empty cells, I wonder why you want to compute type-III tests.

I hope that this is of some help,
 John

  -----------------------------
  John Fox, Professor Emeritus
  McMaster University
  Hamilton, Ontario, Canada
  Web: http::/socserv.mcmaster.ca/jfox