sorry, I still don't understand. By more thinning, do you mean that you are doing a direct comparison of the thickness of G1 to G2? And somehow this changes with threshold?
On 07/16/2014 02:10 PM, Govindarajan, Koushik Athreya wrote:
Dear Doug, Group I shows larger cortical thinning from timepoint 1 to timepoint 2 compared to Group II at p = 0.05. At p = 0.01 and p = 0.001, Group II shows larger cortical thinning from timepoint 1 to timepoint 2 compared to Group I. My question is, why does a change in the threshold affect the trend of cortical thinning between 2 timepoints in the comparable groups?
Thanks a lot for your help Koushik
-----Original Message----- From: freesurfer-bounces@nmr.mgh.harvard.edu [mailto:freesurfer-bounces@nmr.mgh.harvard.edu] On Behalf Of Douglas N Greve Sent: Wednesday, July 16, 2014 12:59 PM To: freesurfer@nmr.mgh.harvard.edu Subject: Re: [Freesurfer] mri_glmfit-sim question
What do you mean that G1 does worse?
On 07/16/2014 11:59 AM, Govindarajan, Koushik Athreya wrote:
Dear Doug, Thanks for writing back. I don't mean the 2 groups should yield same result. I just did not understand how thresholding can change the trend in longitudinal changes. Again, my samples are:
Group I: approx. 120 subjects, timepoint1 and timepoint2 Group II: approx. 120 subjects, timepoint1 and timepoint2
My question is that at p = 0.05, Group I does worse than the other while at p = 0.01 and p = 0.001, it is the other way around.
Thanks Koushik
-----Original Message----- From: freesurfer-bounces@nmr.mgh.harvard.edu [mailto:freesurfer-bounces@nmr.mgh.harvard.edu] On Behalf Of Douglas N Greve Sent: Wednesday, July 16, 2014 10:40 AM To: freesurfer@nmr.mgh.harvard.edu Subject: Re: [Freesurfer] mri_glmfit-sim question
I'm not sure I understand what you mean. Do you expect the two groups to yield the same result?
On 07/16/2014 10:03 AM, Govindarajan, Koushik Athreya wrote:
Dear FS experts,
I am trying to do a paired analysis between 2 time pointsobtained from the longitudinal pipeline and had some trouble interpreting the results. I have 2 different treatment groups I and II. I ran the paired analysis at p = 0.05, p = 0.01 and p = 0.001 vertex-wise thresholds. For p = 0.05, group I shows greater differences between the 2 time points whereas at p = 0.01 and p = 0.001, group II shows greater differences between the 2 time points. Is there any reason that might explain this discrepancy? If not, which result do I trust? The sample size in both groups is comparable (approximately 120 subjects in each group).
Thanks
Koushik
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