Hello, I have come across a result that I cannot explain, and am hoping that
someone else can provide an answer.  A student fitted a mixed model using
the lme function: out<- lme(fixed=Y~A+B+A:B, random=~1|Site).  Y is a
continuous variable while A and B are factors.  The data set is balanced
with the same number of observations in each combination of A and B.  There
are two hierarchical levels: Site and plots nested in site.

 

He tried two different ways of getting theANOVA table: anova(out) and
anova(out, type=”marginal”).

 

Since the data were balanced, these two ways should (I think) give the same
output since they correspond to Type I and III sums of squares in the SAS
terminology.  At least, this is the case with normal (i.e. not mixed) linear
models.  However, he finds very different results of these two types of
ANOVA tables.  Why?

 

Bill Shipley

North American Editor, Annals of Botany

Département de biologie

Université de Sherbrooke

Sherbrooke (Québec) J1K 2R1

Canada

(819) 821-8000, poste 62079

(819) 821-8049 FAX

 

 <http://pages.usherbrooke.ca/jshipley/recherche/>
http://pages.usherbrooke.ca/jshipley/recherche/

 


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