Yes, that is correct for DODS. For DOSS, it is y = e + bi*xi + ci*zi
doug
On 09/03/2013 01:03 PM, ye tian wrote:
Dear Doug,
Would you please let me know what the general formula for the model is for discrete variables x1, x2, .... , xN, covarying with continuous variables z1, z2, ..., zM?
Is it
y = error + bi*xi + cij*xi*zj ?
Otherwise, how does freesurfer decide what model to use?
Thank you very much!
Sincerely,
Ye
On Mon, Aug 19, 2013 at 11:26 AM, Douglas N Greve <greve@nmr.mgh.harvard.edu <mailto:greve@nmr.mgh.harvard.edu>> wrote:
QDEC creates a sentence that describes each contrast. Is that
sentence not clear? I think the only other docs we have for QDEC
are the tutorial.
doug
On 08/19/2013 12:19 PM, ye tian wrote:
Dear Doug,
If I only have two groups, does the statistical test reduce to
a two-tail t-test?
Sorry, I meant to ask what the "default" contrast is, meaning
what the contrast is when I specify no nuisance factor?
Is there an official document where the QDEC setup is gone
over systematically?
Thank you very much!
Sincerely,
Ye
On Mon, Aug 19, 2013 at 11:04 AM, Douglas N Greve
<greve@nmr.mgh.harvard.edu <mailto:greve@nmr.mgh.harvard.edu><mailto:greve@nmr.mgh.harvard.edu <tel:617-724-2358 <tel:617-724-2358>><mailto:greve@nmr.mgh.harvard.edu
<mailto:greve@nmr.mgh.harvard.edu>>> wrote:
-log10(p) which p is the pvalue for the statistical test. The
color is signed by the test.
On 08/19/2013 11:19 AM, ye tian wrote:
Dear Doug,
Would you please shine some light on what quantities
are being
plotted in those statistical maps of QDEC? Some linear
combination of the columns of the design matrix?
Also, what is the "default" design matrix?
Thank you very much!
Sincerely,
Ye
On Tue, Aug 13, 2013 at 11:45 PM, Douglas Greve
<greve@nmr.mgh.harvard.edu
<mailto:greve@nmr.mgh.harvard.edu>
<mailto:greve@nmr.mgh.harvard.edu
<mailto:greve@nmr.mgh.harvard.edu>>
<mailto:greve@nmr.mgh.harvard.edu
<mailto:greve@nmr.mgh.harvard.edu>
<mailto:greve@nmr.mgh.harvard.edu
<mailto:greve@nmr.mgh.harvard.edu>>>> wrote:
1 and 3 are the same model. Calling a variable a
nuisance
factor
is just a description. The model is actually
y = age*meditation*b1 + meditation*b2 + err =
y_hat + err
doug
On 8/13/13 6:12 PM, ye tian wrote:
Dear Freesurfers,
I am studying cortical thickness as a function
of age
(continuous) and meditation practice (categorical,
level1=Normal,
level2=TM). I have three separate cases of qdec,
regression1,
regression2 and regression3.
Regression1: Discrete (Fixed Factor) = meditation;
Continuous
(Covariate) = age
Regression2: Discrete (Fixed Factor) = meditation;
Regression3: Discrete (Fixed Factor) = meditation;
Nuisance
Factor = age
For the question "Does the average thickness
differ
between
Normal and TM?", Regression1 and Regression3 have
identical
result, which is different from Regression2,
i.e., (1
= 3 !=2 ).
May I infer from this result the following
about qdec:
1) Regression1 and Regression3 both fit cortical
thickness,y, to
the model
y = b0 + age*b1 + meditation*b2 + err =
y_hat + err
Regression2 fits:
y = b0 + b2*meditation + err = y_hat + err
2) Some function of y_hat goes into the "average
thickness",
hence the difference between 2 and the others.
However, what role does "Nuisance Factor" play
in this
case?
Thank you very much!
Sincerely,
Ye
_______________________________________________
Freesurfer mailing list
Freesurfer@nmr.mgh.harvard.edu
<mailto:Freesurfer@nmr.mgh.harvard.edu>
<mailto:Freesurfer@nmr.mgh.harvard.edu
<mailto:Freesurfer@nmr.mgh.harvard.edu>>
<mailto:Freesurfer@nmr.mgh.harvard.edu
<mailto:Freesurfer@nmr.mgh.harvard.edu>
<mailto:Freesurfer@nmr.mgh.harvard.edu
<mailto:Freesurfer@nmr.mgh.harvard.edu>>>
https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
_______________________________________________
Freesurfer mailing list
Freesurfer@nmr.mgh.harvard.edu
<mailto:Freesurfer@nmr.mgh.harvard.edu>
<mailto:Freesurfer@nmr.mgh.harvard.edu
<mailto:Freesurfer@nmr.mgh.harvard.edu>>
<mailto:Freesurfer@nmr.mgh.harvard.edu
<mailto:Freesurfer@nmr.mgh.harvard.edu>
<mailto: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.
-- Douglas N. Greve, Ph.D.
MGH-NMR Center
greve@nmr.mgh.harvard.edu <mailto:greve@nmr.mgh.harvard.edu>
Fax: 617-726-7422 <tel:617-726-7422> <tel:617-726-7422
<tel:617-726-7422>>
Bugs: surfer.nmr.mgh.harvard.edu/fswiki/BugReporting
<http://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>
<http://www.nmr.mgh.harvard.edu/facility/filedrop/index.html>
Outgoing:
ftp://surfer.nmr.mgh.harvard.edu/transfer/outgoing/flat/greve/
-- 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/
--
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/