Dear Freesurfers,
I have a question concerning the "nuisance factors" in the qdec dialogue. Suppose I have two independent variables x1 (discrete) and x2 (continuous), and only one observable y. I choose "Discrete (Fixed factor) = x1", "Continuous (covariate) = x2".
If I further chose "Nuisance factor = x2", does that imply that 1) my contrast matrix is (0 1) 2) null hypothesis: Y is independent of x2
Thank you very much!
Sincerely, Ye
Hi Ye, don't select the same factor as nuisance and covariate. It will result in an error for sure. The difference between a covariate and a "nuisance" factor is purely conceptual. By calling something a nuisance you tell QDEC not to create a contrast related to it. doug
On 08/13/2013 02:09 AM, ye tian wrote:
Dear Freesurfers, I have a question concerning the "nuisance factors" in the qdec dialogue. Suppose I have two independent variables x1 (discrete) and x2 (continuous), and only one observable y. I choose "Discrete (Fixed factor) = x1", "Continuous (covariate) = x2". If I further chose "Nuisance factor = x2", does that imply that
- my contrast matrix is (0 1)
- null hypothesis: Y is independent of x2
Thank you very much! Sincerely, Ye
Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
Dear Doug,
I am afraid that I still don't understand why a variable can not be "covarying" and "nuisance" simultaneously.
If variables x1 and x2 are covarying, they both go into the model y = b0 + x1*b1 + x2*b2 + err Is this correct?
Nuisance, however, is related to the contrast, i.e., test hypothesis. If x2 is nuisance, then (1 0) * (x1 x2) = 0 Is this correct?
Otherwise, how does one specify the contrast matrix in Qdec?
Thank you very much!
Sincerely, Ye
On Tue, Aug 13, 2013 at 12:03 PM, Douglas N Greve <greve@nmr.mgh.harvard.edu
wrote:
Hi Ye, don't select the same factor as nuisance and covariate. It will result in an error for sure. The difference between a covariate and a "nuisance" factor is purely conceptual. By calling something a nuisance you tell QDEC not to create a contrast related to it. doug
On 08/13/2013 02:09 AM, ye tian wrote:
Dear Freesurfers, I have a question concerning the "nuisance factors" in the qdec dialogue. Suppose I have two independent variables x1 (discrete) and x2 (continuous), and only one observable y. I choose "Discrete (Fixed factor) = x1", "Continuous (covariate) = x2". If I further chose "Nuisance factor = x2", does that imply that
- my contrast matrix is (0 1)
- null hypothesis: Y is independent of x2
Thank you very much! Sincerely, Ye
Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
-- Douglas N. Greve, Ph.D. MGH-NMR Center greve@nmr.mgh.harvard.edu Phone Number: 617-724-2358 Fax: 617-726-7422
Bugs: surfer.nmr.mgh.harvard.edu/fswiki/BugReporting FileDrop: https://gate.nmr.mgh.harvard.edu/filedrop2 www.nmr.mgh.harvard.edu/facility/filedrop/index.html Outgoing: ftp://surfer.nmr.mgh.harvard.edu/transfer/outgoing/flat/greve/
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The information in this e-mail is intended only for the person to whom it is addressed. If you believe this e-mail was sent to you in error and the e-mail contains patient information, please contact the Partners Compliance HelpLine at http://www.partners.org/complianceline . If the e-mail was sent to you in error but does not contain patient information, please contact the sender and properly dispose of the e-mail.
If x1 and x2 are the same thing, then the equation is non-invertible. If they are the not the same variable, then there is no problem. QDEC computes all the contrasts for you (but excludes contrasts with nuisance variables) doug
On 8/13/13 3:03 PM, ye tian wrote:
Dear Doug,
I am afraid that I still don't understand why a variable can not be "covarying" and "nuisance" simultaneously.
If variables x1 and x2 are covarying, they both go into the model y = b0 + x1*b1 + x2*b2 + err Is this correct?
Nuisance, however, is related to the contrast, i.e., test hypothesis. If x2 is nuisance, then (1 0) * (x1 x2) = 0 Is this correct?
Otherwise, how does one specify the contrast matrix in Qdec?
Thank you very much!
Sincerely, Ye
On Tue, Aug 13, 2013 at 12:03 PM, Douglas N Greve <greve@nmr.mgh.harvard.edu mailto:greve@nmr.mgh.harvard.edu> wrote:
Hi Ye, don't select the same factor as nuisance and covariate. It will result in an error for sure. The difference between a covariate and a "nuisance" factor is purely conceptual. By calling something a nuisance you tell QDEC not to create a contrast related to it. doug On 08/13/2013 02:09 AM, ye tian wrote: > Dear Freesurfers, > I have a question concerning the "nuisance factors" in the qdec > dialogue. Suppose I have two independent variables x1 (discrete) and > x2 (continuous), and only one observable y. I choose "Discrete (Fixed > factor) = x1", "Continuous (covariate) = x2". > If I further chose "Nuisance factor = x2", does that imply that > 1) my contrast matrix is (0 1) > 2) null hypothesis: Y is independent of x2 > Thank you very much! > Sincerely, > Ye > > > _______________________________________________ > Freesurfer mailing list > Freesurfer@nmr.mgh.harvard.edu <mailto:Freesurfer@nmr.mgh.harvard.edu> > https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer -- Douglas N. Greve, Ph.D. MGH-NMR Center greve@nmr.mgh.harvard.edu <mailto:greve@nmr.mgh.harvard.edu> Phone Number: 617-724-2358 <tel:617-724-2358> Fax: 617-726-7422 <tel:617-726-7422> Bugs: surfer.nmr.mgh.harvard.edu/fswiki/BugReporting <http://surfer.nmr.mgh.harvard.edu/fswiki/BugReporting> FileDrop: https://gate.nmr.mgh.harvard.edu/filedrop2 www.nmr.mgh.harvard.edu/facility/filedrop/index.html <http://www.nmr.mgh.harvard.edu/facility/filedrop/index.html> Outgoing: ftp://surfer.nmr.mgh.harvard.edu/transfer/outgoing/flat/greve/ _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu <mailto:Freesurfer@nmr.mgh.harvard.edu> https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer The information in this e-mail is intended only for the person to whom it is addressed. If you believe this e-mail was sent to you in error and the e-mail contains patient information, please contact the Partners Compliance HelpLine at http://www.partners.org/complianceline . If the e-mail was sent to you in error but does not contain patient information, please contact the sender and properly dispose of the e-mail.
Dear Doug,
Thank you very much! Sincerely, Ye
On Tue, Aug 13, 2013 at 11:39 PM, Douglas Greve greve@nmr.mgh.harvard.eduwrote:
If x1 and x2 are the same thing, then the equation is non-invertible. If they are the not the same variable, then there is no problem. QDEC computes all the contrasts for you (but excludes contrasts with nuisance variables) doug
On 8/13/13 3:03 PM, ye tian wrote:
Dear Doug,
I am afraid that I still don't understand why a variable can not be "covarying" and "nuisance" simultaneously.
If variables x1 and x2 are covarying, they both go into the model y = b0 + x1*b1 + x2*b2 + err Is this correct?
Nuisance, however, is related to the contrast, i.e., test hypothesis. If x2 is nuisance, then (1 0) * (x1 x2) = 0 Is this correct?
Otherwise, how does one specify the contrast matrix in Qdec?
Thank you very much!
Sincerely, Ye
On Tue, Aug 13, 2013 at 12:03 PM, Douglas N Greve < greve@nmr.mgh.harvard.edu> wrote:
Hi Ye, don't select the same factor as nuisance and covariate. It will result in an error for sure. The difference between a covariate and a "nuisance" factor is purely conceptual. By calling something a nuisance you tell QDEC not to create a contrast related to it. doug
On 08/13/2013 02:09 AM, ye tian wrote:
Dear Freesurfers, I have a question concerning the "nuisance factors" in the qdec dialogue. Suppose I have two independent variables x1 (discrete) and x2 (continuous), and only one observable y. I choose "Discrete (Fixed factor) = x1", "Continuous (covariate) = x2". If I further chose "Nuisance factor = x2", does that imply that
- my contrast matrix is (0 1)
- null hypothesis: Y is independent of x2
Thank you very much! Sincerely, Ye
Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
-- Douglas N. Greve, Ph.D. MGH-NMR Center greve@nmr.mgh.harvard.edu Phone Number: 617-724-2358 Fax: 617-726-7422
Bugs: surfer.nmr.mgh.harvard.edu/fswiki/BugReporting FileDrop: https://gate.nmr.mgh.harvard.edu/filedrop2 www.nmr.mgh.harvard.edu/facility/filedrop/index.html Outgoing: ftp://surfer.nmr.mgh.harvard.edu/transfer/outgoing/flat/greve/
Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
The information in this e-mail is intended only for the person to whom it is addressed. If you believe this e-mail was sent to you in error and the e-mail contains patient information, please contact the Partners Compliance HelpLine at http://www.partners.org/complianceline . If the e-mail was sent to you in error but does not contain patient information, please contact the sender and properly dispose of the e-mail.
freesurfer@nmr.mgh.harvard.edu
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Douglas N Greve
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ye tian