You can add "--mul 1000" to multiply everything by 1000 which will effectively give you more significant digits. doug
On 12/03/2013 03:36 PM, Kayle Sawyer wrote:
Hi Doug,
Thanks for confirming how to calculate the 95% confidence interval of the slope for all my clusters. I realized that there was a small error in my formula, in that I should use the critical values from the t-distribution, not the z-distribution (so the SE multiplier will be more like 2.0 instead of 1.96, depending on my sample N).
The problem is that mri_segstats trims the output at the 10,000ths place. Here is the cluster.summary and the segstats from the two clusters identified as significantly associated with age.
mc-z.th1.3.neg.sig.cluster.summary: # ClusterNo Max VtxMax Size(mm^2) MNIX MNIY MNIZ CWP CWPLow CWPHi NVtxs Annot 1 -5.096 73213 4275.24 50.0 33.2 -7.2 0.00350 0.00280 0.00430 8455 parstriangularis 2 -3.802 51616 20825.27 4.9 -26.2 39.2 0.00010 0.00000 0.00020 41094 posteriorcingulate
gamma.mgh: # ColHeaders Index SegId NVoxels Volume_mm3 StructName Mean StdDev Min Max Range 1 1 8455 8455.0 Seg0001 -0.0089 0.0027 -0.0147 -0.0038 0.0109 2 2 41094 41094.0 Seg0002 -0.0069 0.0017 -0.0132 -0.0023 0.0108
gammavar.mgh: # ColHeaders Index SegId NVoxels Volume_mm3 StructName Mean StdDev Min Max Range 1 1 8455 8455.0 Seg0001 0.0000 0.0000 0.0000 0.0000 0.0000 2 2 41094 41094.0 Seg0002 0.0000 0.0000 0.0000 0.0000 0.0000
So, for the 95% CI of the slope for cluster #1, I would use these formulas (N=60, so the t-distribution 95% critical value is 2.0003): -0.0089+2.0003*sqrt(0.0000) -0.0089-2.0003*sqrt(0.0000)
Is there any way to add more significant digits to the mri_segstats output?
Thanks, -Kayle
On Nov 4, 2013, at 6:31 PM, Douglas N Greve greve@nmr.mgh.harvard.edu wrote:
Yes, that should work. doug
On 10/30/2013 03:35 PM, Kayle Sawyer wrote:
Hi all,
I would like to calculate the 95% confidence interval of the slope for a thickness cluster (vs age in years) produced by mri_glmfit-sim.
I have obtained values for my clusters from gamma.mgh and gammavar.mgh using these two commands:
mri_segstats --i gamma.mgh --seg mc-z.th1.3.neg.sig.ocn.mgh --excludeid 0 --sum mc-z.th1.3.neg.sig.ocn.gamma.segstats
mri_segstats --i gammavar.mgh --seg mc-z.th1.3.neg.sig.ocn.mgh --excludeid 0 --sum mc-z.th1.3.neg.sig.ocn.gammavar.segstats
Next, (for each cluster, within each segstats summary file) I would take the “mean” from gamma, and the “mean” from gammavar, and calculate the 95% CI thus: gamma + 1.96*sqrt(gammavar) gamma - 1.96*sqrt(gammavar)
Would these two values would give me the 95% confidence interval for the effect of age on that cluster, in mm/year?
Thanks, -Kayle
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