Dear SPM experts,
I have subjects divided into two groups, who are scanned twice (two time points).
I'm interested in the group, time and interaction effect.
(2 x 2 within-subjects ANOVA)
I’ve got the idea from links below, to use 'Flexible Factorial’.
However, I have not been successful in finding clear information about the 2x2 within-subject contrast in the Jiscmail.
- https://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=ind0712&L=spm&D=0&1=spm&9=A&J=on&d=No+Match%3BMatch%3BMatches&z=4&P=340817
- https://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=ind0712&L=spm&D=0&1=spm&9=A&J=on&d=No+Match%3BMatch%3BMatches&z=4&P=369331
- https://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=ind0801&L=spm&D=0&1=spm&9=A&J=on&d=No+Match%3BMatch%3BMatches&z=4&P=157697
The design could be summarized as below. (name / dependency / variance / grand mean scaling (0) / ancova (0))
subject / independent / equal
group / independent / unequal
time / dependent / equal
The two scans from two time points for each subjects are entered as below
eg)
Scans : subj1_pre, subj1_post
Conditions : 1 1; 1 2 (first column represents group, second column represents the timepoint)
For the main effects & interactions
- 1, 2, 3 are given separately as the main effect factor number
- [2 3] is given as the interaction factor numbers
AND For the contrast :
(group1 subjects are entered first)
- N1 : Number of subjects in group 1
- N2 : Number of subjects in group2
Group effect : 1 -1 0 0 1/2 1/2 -1/2 -1/2 repmat(1/N1, 1, N1) repmat(-1/N2, 1, N2)
Time effect : 0 0 1 -1 N1/(N1+N2) -N1/(N1+N2) N2/(N1+N2) -N2/(N1+N2) zeros(1,N1+N2)
Interaction : 0 0 0 0 1 -1 -1 1 zeros(1,N1+N2)
It would be highly appreciated, if anyone with experience in within-subject ANOVA could help confirm or correct above contrast.
Regards,
Kevin
|