[MINC-users] glim_image
Jamila Ahdidan
minc-users@bic.mni.mcgill.ca
Sun Apr 10 03:42:05 2005
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Hi Jason,
Well I have to say that I don't use glim_image to perform a VBM study, but to perform a t test at each voxel to assess the difference between my group of patients and my group of controls. So, I don't really know whether I want to force to be 0 at x=0. (I don't really know what that means!).
Do you think I'm using the wrong minc command, and if yes do you have another idea?
Thanks a lot,
Jamila
Jason Lerch <jason@bic.mni.mcgill.ca> wrote:
On Apr 9, 2005, at 6:51 PM, Jamila Ahdidan wrote:
> My dilema is whether I should just keep
> my good results and forget about the intercept in the
> matrix, or I should stick to the intercept and
> conclude that nothing is interpretable from my
> results.
Is there any reason to force the slope to be 0 at x=0? If you have
standard VBM density data, then that is an invalid assumption, since
there is every reason to allow the y to take on an arbitrary value at
x=0, so you would include that column of ones for your intercept term.
If you have different data then this assumption might be valid -
something that is the case, for example, when looking at asymmetry VBM.
But by and large you will want an intercept.
Hope this helps,
Jason
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<DIV>Hi Jason,</DIV>
<DIV>Well I have to say that I don't use glim_image to perform a VBM study, but to perform a t test at each voxel to assess the difference between my group of patients and my group of controls. So, I don't really know whether I want to force to be 0 at x=0. (I don't really know what that means!).</DIV>
<DIV>Do you think I'm using the wrong minc command, and if yes do you have another idea?</DIV>
<DIV> </DIV>
<DIV>Thanks a lot,</DIV>
<DIV>Jamila<BR><BR><B><I>Jason Lerch <jason@bic.mni.mcgill.ca></I></B> wrote:</DIV>
<BLOCKQUOTE class=replbq style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #1010ff 2px solid"><BR>On Apr 9, 2005, at 6:51 PM, Jamila Ahdidan wrote:<BR><BR>> My dilema is whether I should just keep<BR>> my good results and forget about the intercept in the<BR>> matrix, or I should stick to the intercept and<BR>> conclude that nothing is interpretable from my<BR>> results.<BR><BR>Is there any reason to force the slope to be 0 at x=0? If you have <BR>standard VBM density data, then that is an invalid assumption, since <BR>there is every reason to allow the y to take on an arbitrary value at <BR>x=0, so you would include that column of ones for your intercept term. <BR>If you have different data then this assumption might be valid - <BR>something that is the case, for example, when looking at asymmetry VBM. <BR>But by and large you will want an intercept.<BR><BR>Hope this
helps,<BR><BR>Jason<BR><BR>_______________________________________________<BR>MINC-users@bic.mni.mcgill.ca<BR>http://www.bic.mni.mcgill.ca/mailman/listinfo/minc-users<BR></BLOCKQUOTE><p>
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