Ah sorry for the low level of info. I am aiming to do a simple group comparison, where I'm comparing thickness between controls and obese or T2DM patients, regressing out the effect of age, sex and, hypertension. So I created one thickness file with fwhm 10 containing all participants of the 3 groups. The contrast file looks like this:
1 0 -1 0 0 0 for controls vs T2DM 1 -1 0 0 0 0 for controls vs obese 0 1 -1 0 0 0 for obese vs T2DM, although there I do not expect something to happen And the GLM works fine (differences in the first and second contrast), but I was wondering whether the fact that the groups are unbalanced might influence the results in some way. Thanks, Eelco 2016-10-13 11:17 GMT-03:00 Bruce Fischl <fis...@nmr.mgh.harvard.edu>: > Hi Eelco > > it depends on how you setup your GLM. Are you trying to regress out the > effects of obesity in some way? If you give us more details I expect > someone else can answer your question (Doug!) > > > cheers > Bruce > > > On Thu, 13 Oct 2016, Eelco van Duinkerken wrote: > > Thanks for the quick reply! >> So if I understand correctly, the power of say the controls vs. diabetes >> (indeed it is type 2 diabetes) comparison is constrained by the sample >> size >> of the obese group? >> >> 2016-10-13 11:02 GMT-03:00 Bruce Fischl <fis...@nmr.mgh.harvard.edu>: >> Hi Eelco >> >> it isn't really a question of whether our implementation is >> senstitive to >> this. It's that in general your power will be constrained by the >> size of >> the smaller group (I assume this is Type 2 diabetes by the way). >> >> cheers >> Bruce >> >> >> On Thu, 13 Oct 2016, Eelco van Duinkerken wrote: >> >> > Hi all, >> > I am using FS with data from 2 different studies that were >> acquired on the >> > same MRI-machine with the same T1 and FLAIR sequences. >> Unfortunately, the >> > group sizes are not very balanced, with 31 controls, 16 obese >> and 32 >> > diabetes patients. >> > >> > Is the GLM for thickness used in FS very sensitive to this >> unequal group >> > size? >> > >> > >> > Thanks for the help, >> > >> > Eelco >> > >> > >> _______________________________________________ >> 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. >> >> >> >> >> -- >> Eelco van Duinkerken, PhD >> Pontifícia Universidade Católica | Department of Psychology | >> R. Marquês de São Vicente 225 | Gávea, Rio de Janeiro - RJ | CEP >> 22451-900 | >> Brasil | >> E-mail: e.vanduinker...@vumc.nl | Phone: +55-21-35271855 | >> http://lattes.cnpq.br/7180895567820901 >> & >> VU University Medical Center | Department of Medical Psychology | >> De Boelelaan 1117 | 1081 HV | Amsterdam | The Netherlands >> >> > _______________________________________________ > 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. > > -- Eelco van Duinkerken, PhD Pontifícia Universidade Católica | Department of Psychology | R. Marquês de São Vicente 225 | Gávea, Rio de Janeiro - RJ | CEP 22451-900 | Brasil | E-mail: e.vanduinker...@vumc.nl | Phone: +55-21-35271855 | http://lattes.cnpq.br/7180895567820901 & VU University Medical Center | Department of Medical Psychology | De Boelelaan 1117 | 1081 HV | Amsterdam | The Netherlands
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