On 01/02/15 02:17, John Sorkin wrote:
I am trying to understand the Error function and its use in ANOVA. In
particular I want to understand the difference between two models
that differ only with respect to the Error statement:
aovsubj <- aov(value~group+time+Error(subject),data=dataRMANOVA)
and
aovsubjgroup <- aov(value~group+time+Error(subject/group),data=dataRMANOVA)
You will note that in my data I have two subject identifiers,
subject and subject2. I am also trying to trying to understand how I
should identify subjects, within group (i.e. intervention vs.
control) or within time (0=baseline, 1=post)
Since no-one else seems to have answered you let me point out that your
first formulation treats subject 1 in the "int" group as being the same
as subject 1 in the "cont" group, and similarly for subject 2 and so on.
The second formulation (subject nested within group) treats subject 1 in
the "int" group as being *different* from subject 1 in the "cont" group.
If you were using subject2 instead of subject there would (I *think*) be
no difference between the two formulations.
HTH
cheers,
Rolf Turner
--
Rolf Turner
Technical Editor ANZJS
Department of Statistics
University of Auckland
Phone: +64-9-373-7599 ext. 88276
Home phone: +64-9-480-4619
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