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 <gr...@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 < >> gr...@nmr.mgh.harvard.edu >> <mailto:gr...@nmr.mgh.harvard.**edu<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<gr...@nmr.mgh.harvard.edu> >> > >> <mailto:gr...@nmr.mgh.harvard.**edu <gr...@nmr.mgh.harvard.edu> >> >> <mailto:gr...@nmr.mgh.harvard.**edu <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:freesur...@nmr.mgh.**harvard.edu<Freesurfer@nmr.mgh.harvard.edu> >> > >> >> <mailto:freesur...@nmr.mgh.**harvard.edu<Freesurfer@nmr.mgh.harvard.edu> >> >> >> <mailto:freesur...@nmr.mgh.**harvard.edu<Freesurfer@nmr.mgh.harvard.edu> >> >> >> https://mail.nmr.mgh.harvard.**edu/mailman/listinfo/** >> freesurfer <https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer> >> >> >> >> ______________________________**_________________ >> Freesurfer mailing list >> Freesurfer@nmr.mgh.harvard.edu >> >> <mailto:freesur...@nmr.mgh.**harvard.edu<Freesurfer@nmr.mgh.harvard.edu> >> > >> >> <mailto:freesur...@nmr.mgh.**harvard.edu<Freesurfer@nmr.mgh.harvard.edu> >> >> >> <mailto:freesur...@nmr.mgh.**harvard.edu<Freesurfer@nmr.mgh.harvard.edu> >> >> >> >> >> https://mail.nmr.mgh.harvard.**edu/mailman/listinfo/**freesurfer<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<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<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> >> >> <http://surfer.nmr.mgh.**harvard.edu/fswiki/**BugReporting<http://surfer.nmr.mgh.harvard.edu/fswiki/BugReporting> >> > >> FileDrop: >> https://gate.nmr.mgh.harvard.**edu/filedrop2<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<http://www.nmr.mgh.harvard.edu/facility/filedrop/index.html> >> > >> Outgoing: >> >> ftp://surfer.nmr.mgh.harvard.**edu/transfer/outgoing/flat/**greve/<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<http://surfer.nmr.mgh.harvard.edu/fswiki/BugReporting> > FileDrop: > https://gate.nmr.mgh.harvard.**edu/filedrop2<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/ <ftp://surfer.nmr.mgh.harvard.edu/transfer/outgoing/flat/greve/> > >
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