Paired (aka. Repeated measures, aka. within-Ss) tests can be achieved
by using aov() and specifying the within-Ss effect in the error term:
my_aov = aov( dependent_variable~between_Ss_variable*within_Ss_variable
+ Error(Ss_id/(within_Ss_variable)))
summary(my_aov)
On Mon, Apr 20, 2009 at 10:25 AM, A Ezhil <ezhil02 at yahoo.com>
wrote:>
> Hi,
>
> I have an experimental data with 2 factors: visit and treatment. Each
subject has 2 visits and on each visit they get a treatment. We take samples
before and after treatment. I can easily to do the 2-way ANOVA in R with visit
and treatment as factors.
>
> anova( lm(data ~ visit*treatment) )
>
> If I want to do the same 2-way ANOVA for the paired samples, how can I do
that? Is there any R packages for that?
>
> Thanks in advance.
>
> Kind regards,
> Ezhil
>
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--
Mike Lawrence
Graduate Student
Department of Psychology
Dalhousie University
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~ Certainty is folly... I think. ~