Thanks much Dough for your reply.

So if I add another column Performance*Age (after removing the mean of each) in my fsgd file (and remove individual columns for Performance and age), could you please tell what will be the contrast matrix (after only Gender as a covariate) in that case i.e. for following fsgd:

Class Male
Class Female
Variables Perform*Age
Input S1 Male 180
Input S2 Female 167

Thanks.

On Mon, Feb 26, 2018 at 2:31 PM, Douglas N Greve <greve@nmr.mgh.harvard.edu> wrote:


On 02/24/2018 12:00 AM, Martin Juneja wrote:
> Hi experts,
>
> I am not sure if this has already been addressed in FS discussion.
>
> If my fsgd file looks like following:
>
> Class Male
> Class Female
> Variables Performance Age
> Input S1 Male 181 25
> Input S2 Female 167 23
> ....
> ....
>
> I understand that the contrast matrix *[**0 0 1 -1 0 0]* represents
> whether there is a difference between the group
> (male/female)-performance slopesregressing out the effect of age. In
> other words, this matrix calculates whether two slopes i.e. one for
> males: thickness-performance slope and second for females:
> thickness-performance slope - are significantly different after
> regressing out the effect of age.
>
> My questions are following:
>
> (1) Is my above interpretation of contrast matrix*[**00 1 -1 0
> 0]* correct?
Yes
> (2) If my interpretation is correct, then I was wondering what will be
> the contrast matrix if *I want to check whether there is **significant
> effect of age on e.g. thickness-performance slopes after regressing
> out the effect of gender.* And what will be the corresponding fsgd
> file for that, any changes in that?
This is an interaction between continuous variables, which can be a
little tricky. You cannot do it with the model that you have. The
typical way to do this  is to create a third covariate which is the
product of Performance*Age; you should remove the mean of Performance
and Age before doing the product.
>
> Thanks.
>
>
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Douglas N. Greve, Ph.D.
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