you need to have all 3. If you want to examine the interaction, then you
need a new contrast to test the interaction. Set all to 0 except for the
interaction term
doug
On 08/22/2013 10:42 AM, Jacobs H (NP) wrote:
Dear Doug,
Thank you for the information. Sorry for not sending this to the list.
Do you mean that I then have to include the three variables (covariate 1,
covariate 2, product of these two) or only the product in the fsgd file?
If I need to include all three of them, can you advise me on the contrasts?
If it is only the product, I think I can use the same contrasts as before,
right?
Thanks
Heidi
Dr. Heidi Jacobs
Postdoc researcher
Faculty of Health, Medicine and Life Sciences
School for Mental Health and Neurosciences
Division Cognitive Neuropsychiatry and Clinical Neurosciences
Alzheimer Center Limburg
h.jac...@maastrichtuniversity.nl
www.maastrichtuniversity.nl
www.heidijacobs.nl
Dr. Tanslaan 12, 6229 ET Maastricht
P.O. Box 616, 6200 MD Maastricht, The Netherlands
T +31 43 38 84 090 F +31 43 38 84 092
Van: freesurfer-boun...@nmr.mgh.harvard.edu
[freesurfer-boun...@nmr.mgh.harvard.edu] namens Douglas N Greve
[gr...@nmr.mgh.harvard.edu]
Verzonden: donderdag 22 augustus 2013 16:34
Aan: freesurfer@nmr.mgh.harvard.edu
Onderwerp: Re: [Freesurfer] Contrast and F-test
If you want to test for an interaction between continuous variables,
then you should create a new regressor by multiplying them together then
test that regressor
doug
On 08/22/2013 08:09 AM, Jacobs H (NP) wrote:
Hi all,
I my manuscript, I examined the association between cognition and cortical
thickness. I first did this in three groups separately and then ran a F-test.
One of the reviewers, now wants me to examine the interaction between
cognition and education (all continuous).
Would this be the correct contrast for each group separately (last two zeros
are for covariates, also continuous)
0 1 -1 0 0
Would this be the correct way for the F-test:
0 0 0 0 0 1 -1 0 -1 1 0 0 0 0 0 0 0
0 0 0 1 0 -1 -1 0 1 0 0 0 0 0 0
Thanks!
Heidi
Dr. Heidi Jacobs
Postdoc researcher
Faculty of Health, Medicine and Life Sciences
School for Mental Health and Neurosciences
Division Cognitive Neuropsychiatry and Clinical Neurosciences
Alzheimer Center Limburg
h.jac...@maastrichtuniversity.nl
www.maastrichtuniversity.nl
www.heidijacobs.nl
Dr. Tanslaan 12, 6229 ET Maastricht
P.O. Box 616, 6200 MD Maastricht, The Netherlands
T +31 43 38 84 090 F +31 43 38 84 092
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