Re: [Freesurfer] GLM in groups with unequal size

2016-10-14 Thread Douglas Greve
It will not On 10/13/16 10:34 AM, Eelco van Duinkerken wrote: 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 t

Re: [Freesurfer] GLM in groups with unequal size

2016-10-14 Thread Douglas Greve
It will be constrained by the group with the smaller number of subjects. There is not anything wrong with unequal group sizes, but it is less efficient than if you had split your acquisitions evenly. On 10/13/16 10:17 AM, Bruce Fischl wrote: Hi Eelco it depends on how you setup your GLM. A

Re: [Freesurfer] GLM in groups with unequal size

2016-10-13 Thread Eelco van Duinkerken
Thank you Jurgen! That helps a lot. Good to know that the results are not driven by any difference in varience. Thanks all, Eelco 2016-10-13 12:00 GMT-03:00 Juergen Haenggi : > Dear Eelco > > years ago i posed a similar question on the FS email list > > https://mail.nmr.mgh.harvard.edu/pipermai

Re: [Freesurfer] GLM in groups with unequal size

2016-10-13 Thread Juergen Haenggi
Dear Eelco years ago i posed a similar question on the FS email list https://mail.nmr.mgh.harvard.edu/pipermail//freesurfer/2011-November/021386.html a part of the response is below >>> The other question is how mri_glmfit estimates the variance. Because I have >>> only one subject in the patie

Re: [Freesurfer] GLM in groups with unequal size

2016-10-13 Thread Eelco van Duinkerken
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 grou

Re: [Freesurfer] GLM in groups with unequal size

2016-10-13 Thread Eelco van Duinkerken
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 : > Hi Eelco > > it isn't really a question of whether our

Re: [Freesurfer] GLM in groups with unequal size

2016-10-13 Thread Bruce Fischl
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! S

Re: [Freesurfer] GLM in groups with unequal size

2016-10-13 Thread Bruce Fischl
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,