Hi Bruce,
Thank you very much for your prompt and helpful answer.
I have one more question, please: I do not understand what's the role of adding the threshold value while running the mri_glmfit-sim with --cache since after adding the threshold 2, I still get clusters with cwp>.01.
This is what I was running:
mri_glmfit-sim \ --glmdir rh.age.glmdir \ --cache 2 neg \ --cwpvalthresh .025 \ --overwrite
And this is my output:
# ClusterNo Max VtxMax Size(mm^2) MNIX MNIY MNIZ CWP CWPLow CWPHi NVtxs Annot
1 -6.24 104279 2004.41 6.4 -83.6 34.4 0.0001 0 0 3539 cuneus
2 -5.71 56656 2923.03 24.4 25.4 37.1 0.0001 0 0 5020 superiorfrontal
3 -4.89 156133 1826.82 5.1 -29.7 38.6 0.0001 0 0 4324 posteriorcingulate
4 -4.57 117278 1917.42 43.2 43.4 -8.2 0.0001 0 0 3393 parsorbitalis
5 -4.32 134603 910.13 10.5 45.7 -9.2 0.0009 0 0 1597 medialorbitofrontal
6 -4.01 47845 1018.06 38.9 -73.9 34.6 0.0003 0 0 1802 inferiorparietal
7 -3.97 12268 580.81 14.2 -51 63.3 0.0132 0.01 0.01 1415 superiorparietal
8 -3.78 54798 871.02 53 -39.7 -5.1 0.0010 0 0 1969 bankssts
9 -3.78 21941 555.51 45.8 -28.2 6.4 0.0175 0.02 0.02 1369 superiortemporal
10 -2.91 86118 884.25 10.1 -98.9 11.7 0.0010 0 0 1089 lateraloccipital
11 -2.86 13271 674.26 21.5 -65.4 -6.1 0.0056 0 0.01 722 lingual
Is this right? Also, by adding for the lh --cwpvalthresh .025 what exactly means or how the corrections are made for both hemispheres. I know --cwpvalthresh .025 shows only clusters p<.025 but then what means cluster significance values not corrected for 2 spaces?
Please advise.
Thank you. Antonella
________________________________ From: Douglas N Greve greve@nmr.mgh.harvard.edu To: Antonella Kis atorok9@yahoo.com Cc: "freesurfer@nmr.mgh.harvard.edu" freesurfer@nmr.mgh.harvard.edu Sent: Tuesday, August 23, 2011 4:33 PM Subject: Re: [Freesurfer] correction for multiple comparisons
Yes, that is correct, you should use .025 if you are correcting for both hemispheres. doug
Antonella Kis wrote:
Hi Doug,
I would like to run the correction for multiple
comparisons. I know
glmfit-sim corrects for multiple comparisons. My question is:
the corrections for multiple comparisons will be done while running
mri_glmfit-sim \ --glmdir rh.age.glmdir \ --cache 2 neg \ --overwrite
or I need to add --cwpvalthresh .025 before --overwrite. I found on-line that setting a treshold = 2 means p < 0.05 but adding --cwpvalthresh .025 will do the correction across 2 spaces: lh and rh: .025 = .05/2 Bonferroni Correction and will show only the clusters with p<.025. Is this right? So to run for multiple corrections in fact I will need to run:
mri_glmfit-sim \ --glmdir rh.age.glmdir \ --cache 2 neg \ --cwpvalthresh .025 --overwrite
Please advise me.
Thank you for your time and
help.
Antonella
*From:* Douglas N Greve greve@nmr.mgh.harvard.edu *To:* Antonella Kis atorok9@yahoo.com *Cc:* "freesurfer@nmr.mgh.harvard.edu" freesurfer@nmr.mgh.harvard.edu *Sent:* Monday, August 22, 2011 2:28 PM *Subject:* Re: [Freesurfer] GLM or Qdec ?
Antonella Kis wrote:
Dear FS experts,
I finished running the GLM and I wonder what is the best way to further
analyse my data in order to see if there is any relation
between age (at seizure onset) and cortical thickness for my patients versus control group.
1). Why when I overlay the sig.mgh in tksurfer lh inflated, I get more clusters than the number of clusters obtained from mri_glmfit-sim?
When you look at it in tksurfer, you are looking at uncorrected data. glmfit-sim corrects for multiple comparisons. Some of the clusters don't survive.
2). What sig.mgh represents?
-log10(p)
- What's the real significance of a cluster (how a cluster is formed)?
It is based on the likelihood of getting a cluster of that size by chance given the search space (cortical surface area), smoothness (FWHM), and cluster-forming threshold (eg, p<.05).
4). Why my thickness value in clusters (eg cluster no. 1 which
coresponds to the posteriorcingulate) for subject no.1 is different that the thickness value obtained for the same region in the lh.aparc.stats while running recon-all?
5). After running the GLM should I use visualizing and plotting method to further analyse my data and load FSGD file lh.gender_age.glmdir/y.fsgd?
6). Should my ROI's be defined or be the same with my clusters?
I don't know what you mean by that.
7). What is the difference between GLM and Qdec? What method is the best to analyse the relation between age and cortical thickness for my patients versus control group?
They are the same statistically. They are just different ways to provide information about your design
and contrasts. QDEC is graphical (point
and click). mri_glmfit you create FSGD files and run it from the command-line. QDEC actually creates FSGD files and contrast files and runs mri_glmfit.
8). Why when analysing with Qdec I get more clusters? Are this defining or representing the sig.mgh as in GLM?
They should give identical results when run in the same way. My guess is that you have created two different designs and so are getting different answers.
9). When using Qdec were I can find as an output of results the number of clusters and the cortical thickness value?
You'll have to run the correction for multiple comparisons (interface on the results page). This simply runs mri_glmfit-sim.
doug
Thank you and have a great day!
Antonella
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