I am trying to conduct a higher level FEAT analysis (FLAME 1) comparing
change in activation on two separate scans (i.e. pre & post treatment)
between 3 different treatment groups. Participants underwent 3 runs during
each scanning session in which three different types of videos were
presented numerous times in a randomized fashion.
First level Voxel-wise GLM analysis was conducted (using custom timing
files) to compare parameter estimates (PE) of the hemodynamic response to
the three video conditions versus each of the other and rest for each run.
Next, voxel-wise, fixed effects GLM analyses was conducted individually for
each participant to determine the relative activation over the three
identical runs in each session (pre & post).
Below I have included a design matrix and contrasts intended to examine
differences in the change from pre to post treatment (relative to each video
condition) between the 3 treatment groups. Inputs are from level 2 fixed
effects analysis.
Input group EV1 EV2 EV3 EV4 EV5 EV6 EV7 EV8 EV9 EV10
1-pre 1 1 1
2-pre 1 1 1
3-pre 1 1 1
1-post 1 -1 1
2-post 1 -1 1
3-post 1 -1 1
…
4-pre 2 1 1
5-pre 2 1 1
6-pre 2 1 1
4-post 2 -1 1
5-post 2 -1 1
6-post 2 -1 1
…
7-pre 3 1 1
8-pre 3 1
9-pre 3 1
7post 3 -1 1
8-post 3 -1
9-post 3 -1
…
Contrasts EV1 EV2 EV3 EV4 EV5…
C1. All (pre-post) 1 1 1 0 0
C2. All (post-pre) -1 -1 -1 0 0
C3. Group 1 (pre-post) 1 0 0 0 0
C4. Group 1 (post-pre) -1 0 0 0 0
C5. Group2 (pre-post) 0 1 0 0 0
…
C6. Grp1>Grp2 (pre-post) 1 -1 0 0 0
C7. Grp2>Grp1 (pre-post) -1 1 0 0 0
C8. Grp1>Grp3 (pre-post) 1 0 -1 0 0
C9. Grp3>Grp1 (pre-post) -1 0 1 0 0
…
My primary concern with this design centers around the between group
analysis. It seems that when comparing groups with the contrast above an
inversion of the pre/post relationship will occur leading to a [Group1
(pre-post)] – [Group2 (post-pre)] comparison in the case of C6. Is this the
case? and if so is there a better method to analyze group differences in
change from pre to post treatment?
Thanks for the help.
Chris Culbertson
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