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. 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 fischl@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 > >
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-- 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.vanduinkerken@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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