On 02 Feb 2015, at 13:09 , S Ellison <s.elli...@lgcgroup.com> wrote:
>
>>> aovsubj <- aov(value~group+time+Error(subject),data=dataRMANOVA)
>>> and
>>> aovsubjgroup <- aov(value~group+time+Error(subject/group),data=dataRMANOVA)
>>>
>> 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.
>
> Yes, but that isn't all, is it?
>
> subject/group
>
> means group nested in subject, expanding to
> ~subject+subject:group.
>
> so Error(subject/group) asks for a subject effect across groups _as well as_
> one within groups.
>
Or maybe more usefully stated, a group effect within subjects. This could be
relevant if each individual goes to two different groups labeled say 1 and 2,
but the groups are not related between different subjects (subj.1 attends AA
and Boy Scouts, subj 2 School Board and Church, etc.) so there is no main
effect of group. In statistics, it is usually the other way around: subjects
arbitrarily numbered 1-20 within each group, but no relation between "subj.1"
in one group and "subj.2" of the other, in which case ~group +
Error(group:subject) makes sense.
> S Ellison
>
>
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