Dear SPMers,
I have analyzed my data using both the flexible factorial option in SPM and GLM flex and the results seem to be very different. Does this mean I did something wrong?
I have a 2x2x2 within-subject design and 20 subjects.
In GLM Flex I did:
IN.N_subs = [20];
IN.Within = [2 2 2];
IN.WithinLabs = {{‘F1L1’ ‘F1L2’} {‘F2L1’ ‘F2L2’} {‘F3L1’ ‘F3L2’}};
IN.Interactions = {[1 2] [1 3] [2 3] [1 2 3]};
IN.FactorLabs = {‘Factor1’ ‘Factor2’ ‘Factor3’};
IN.EqualVar = [1 1 1];
IN.Independent = [0 0 0];
F = CreateDesign(IN);
I.OutputDir = pwd;
I.F = F;
I.minN = 19;
I.DoOnlyAll = 1;
I.RemoveOutliers=0;
I.Scans = {s1_ess_001.img, ..., s20_ess_008.img}
In SPM flexible factorial:
Factors (in this order of entry):
subject
F1
F2
F3
Conditions (in Subjects field):
1 1 1
1 1 2
1 2 1
1 2 2
2 1 1
2 1 2
2 2 1
2 2 2
Scans were entered, for each subject, in this order: ess_001.img,..,ess_008.img, which correspond to the order of the conditions above
Main effects & Interactions:
Main effects (factor numbers)
1
2
3
4
Interactions
[2;3]
[2;4]
[3;4]
When I compare the main effect of say factor F2 using GLM Flex
I.Cons(2).Groups = {3 4};
I.Cons(2).Levs = [2];
I.Cons(2).ET = 3;
I.Cons(2).mean = 0;
and SPM
[0 0 -1 1 0 0 0.5 -0.5 0.5 -0.5 0 0 0 0 0.5 0.5 -0.5 -0.5]
the results look totally different although I'm testing the same main effect (i.e., main effect of F2).
Could someone please tell me if the analyzes above are correct and the reason for the different resulting maps?
Thank you in advance,
Angela
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