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.jacobs@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-bounces@nmr.mgh.harvard.edu [freesurfer-bounces@nmr.mgh.harvard.edu] namens Douglas N Greve [greve@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.jacobs@maastrichtuniversity.nl www.maastrichtuniversity.nl www.heidijacobs.nl
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