Hi Doug, I'm jumping in the discussion because I was a bit scared with your previous email mentioning that this DOSS bug affects all FreeSurfer's versions. Does that also affect statistical analyses computed with mri_glmfit using the command line? Do you have an insight whether the bias introduced by the bug is important or not? (as others may also be, I'm becoming a bit anxious about previously published results…)
Finally, to get back to Elisa's question: do you have some suggestion in the mean time to assess the relationship between cortical thickness and a clinical measure correcting for age and gender? Using DODS? With or without demeaning the covariates and nuisance? Sorry for the abundance of questions, and, as always, thanks a lot for your answer! Marie On Sep 20, 2013, at 6:13 PM, Douglas N Greve <gr...@nmr.mgh.harvard.edu> wrote: > > Hi Elisa, don't use the DOSS feature in QDEC. Sorry, I sent out an email > about 6mo ago on this, but it is not easy to let people know about a bug > once the bug is out there. > doug > > > On 09/19/2013 11:30 AM, E. Scariati wrote: >> Dear Freesurfer experts, >> >> I would like to study the relationship between cortical thickness and >> one clinical variable with qdec, but correcting for age and gender. >> >> Given that I have only one group and 2 covariates (one continuous, one >> dichotomic) I don't know how I should set the design of my analysis in >> qdec, especially for the gender variable. >> >> I have tried two different ways (both DOSS design): >> >> 1) selecting Discrete = gender; Continuous = clinical measure; >> Nuisance factor = age >> and looking at the contrast called : "Does the correlation between >> thickness and clinical measure accounting for gender differ from 0? >> nuisance factor : age" >> >> 2) selecting : continuous = clinical measure; Nuisance Factor = age, >> gender (coded as 1 and 2) >> and looking at the contrast called : "Does the correlation >> between thickness and clinical measure differ from 0, nuisance factor >> : age, gender" >> >> But the two contrasts give very different results, which I find very >> surprising. I exported cortical thickness at the peak significance of >> the clusters and tried to run a GLM myself in SPSS and it seems that >> coding gender as a continuous variable with two values (1 and 2) >> provides the most realistic results. However, I saw many times on the >> mailing list that you recommend to use gender as a discrete variable, >> so I am very confused. >> Could you explain me the difference between these contrasts and help >> me to identify which one will accurately identify the correlation >> between cortical thickness and my clinical variable correcting for the >> effect of age and gender. >> >> Thank you in advance for your answer, >> Best regards >> Elisa >> >> >> _______________________________________________ >> 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 > 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 > > > 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 mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
