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 > <gr...@nmr.mgh.harvard.edu <mailto:gr...@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 > <gr...@nmr.mgh.harvard.edu <mailto:gr...@nmr.mgh.harvard.edu> > <mailto:gr...@nmr.mgh.harvard.edu > <mailto:gr...@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>> > 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>> > > 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 > gr...@nmr.mgh.harvard.edu <mailto:gr...@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 gr...@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
