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Thanks Donald.
Ok, I can see how that would work, but doesn’t this sort of
limit you to just 3 factors or less? It doesn’t seem like the flexible
factorial method has that limitation.
-John
From: MCLAREN, Donald
[mailto:[log in to unmask]]
Sent: Friday, October 31, 2008 4:41 PM
To: West, John D.; SPM
Subject: Re: [SPM] Flexible factorial design error
Since you have specified
"All Scans", you need a factor matrix with 4 columns. There is no way
for SPM to know which scans go with which subject if you leave it out. If you
choose the other option, then you specify the other levels on a subject by
subject basis and thus there is explicit knowledge of which scans go with which
subjects.
Column 1: should list the observation/row number
Column 2: factor 1 level
Column 3: factor 2 level (if no factor 2, use 1s)
Column 4: factor 3 level (if no factor 3, use 1s)
e.g.
1 1 1 1
2 1 1 2
3 1 1 3
4 2 1 1
5 2 1 2
...
16 6 2 1
17 6 2 2
18 6 2 3
...
...
27 9 3 3
Hope this helps.
On Fri, Oct 31, 2008 at 3:21 PM, West, John D. <[log in to unmask]> wrote:
Hello.
I am following Glascher and Gitelman's guide for flexible factorial design and
have run into a snag.
I am trying to set up a 3x3 factorial design where I have three groups and
three time points. I want to include the main effects of subject, group,
time and groupxtime interaction.
So I set up factors for subject, group, time and choose to specify all scans
and factor matrix.
I have input the subjects list in order of group then time. Therefore my
factor matrix should be (since the subject factor does not have to be specified
as it is a special factor):
Group 1:
1 1
1 2
1 3
1 1
1 2
1 3
Etc.
Group 2:
2 1
2 2
2 3
2 1
2 2
2 3
Etc.
Group 3:
3 1
3 2
Etc.
Then I set three main effects for subject, group, and time, and the interaction
of group x time.
This seems to be the right way to set things up but when I go to run this and
create the design matrix I get the following:
Error: factor matrix must have four columns.
I am not sure why I get this error as I should not need four columns (I only
have three factors overall and the subject factor should not need to be set).
Can anybody tell me where I might be going wrong?
Thanks in advance for the help!
-John West
IU School of Medicine
--
Best Regards, Donald McLaren
=====================
D.G. McLaren
University of Wisconsin - Madison
Neuroscience Training Program
Office: (608) 265-9672
Lab: (608) 256-1901 ext 12914
Cell: (773) 406 2464
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