[R] Post-hoc t-tests in 2-way repeated measure ANOVA

Giuseppe Pagnoni gpagnon at emory.edu
Mon Aug 30 18:14:08 CEST 2004

Hi all

I will repost this since it seems to me such a common problem and I 
couldn't find any solution in the mail list...

I am running a 2-way repeated measure anova with 1 between-subjects
factor (Group=treatment, control), and 1 within-subject factor (Time of
measurement: time1, time2).  I extract the results of the anova with:

summary(aov(effect ~ Group*Time + Error(Subj/Time), data=mydata))

following the notes of Jonathan Baron.

Now,is there a way in R to quickly extract all the post-hoc t-tests for 
the simple main effects, corrected of course for multiple comparisons?

Group1 at Time1 vs Group1 at Time2
Group2 at Time1 vs Group2 at Time2

Group1 at Time1 vs Group2 at Time1
Group1 at Time2 vs Group2 at Time2

Also, how can I enter in the model formula a counfounding
covariate (e.g., Age)?

thanks in advance for any suggestions!


Giuseppe Pagnoni, Ph.D.
Dept. of Psychiatry and Behavioral Sciences
1639 Pierce Drive, Suite 4000
WMB Bldg., Atlanta, GA 30322, U.S.
phone: 404-712-8431
fax: 404-727-3233
e-mail: gpagnon at emory.edu

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