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Hello Donald and SPM users,

I am trying to run a flexible factorial model but I keep getting the following error. 
Error using ==> spm_meanby at 31
row dimension mismatch between inputs

I think the problem is how I am defining the Factor Matrix but not sure.  I would appreciate any help.

Here is how the model is set up.
I have three groups (n1=4, n2=16, n3=6)  and two conditions (pre- and post-).  Therefore, I have a total of 52 scans.

I have included three factors in the model: SUBJECT, GROUP and CONDITION.
SUBJECT: independence-yes, variance-equal
GROUP: independence-yes, variance-unequal
CONDITION: independence-no, variance-equal

I specified three main effects (one for each factor) and the interaction between GROUP and CONDITION.

I specified all Scans (52), therefore the Factor Matrix (52 x 4) was defined as
1   1   1   1
1   1   1   2
1   2   1   1
1   2   1   2
1   3   1   1
1   3   1   2
1   4   1   1
1   4   1   2
1   5   2   1
1   5   2   2
...
1  23   3   1
1  23   3   2
1  24   3   1
1  24   3   2
1  25   3   1
1  25   3   2
1  26   3   1
1  26   3   2

I also tried to define the first column as the number of observation, i.e. 1 2 3 4 5 6 ... 52 but still does not work.

Thank you,
Bedda



On Tue, Sep 6, 2011 at 6:52 PM, MCLAREN, Donald <[log in to unmask]> wrote:
I'm not sure when this change happened, but I know there are several
posts from me and others where the FlexFact model was specified as:
column 1: 1 to N
column 2: factor 1 levels
column 3: factor 2 levels
column 4: factor 4 levels

In the current release, the first column should be set to 1s.

Otherwise, the covariances are not estimated.

If anyone thinks this is incorrect, please correct me.

Best Regards, Donald McLaren
=================
D.G. McLaren, Ph.D.
Postdoctoral Research Fellow, GRECC, Bedford VA
Research Fellow, Department of Neurology, Massachusetts General Hospital and
Harvard Medical School
Office: (773) 406-2464
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