Dear experts,

I am now doing some rsFC analyses among individuals with Internet addiction and controls and trying to exmaine the differences between these two groups. Unfortunately, no clusters remained after FDR corrected. Although there remains some significant results if I used Alphasim correction instead, I found that Alphasim correction might be doubted by some reviewers and was rarely used in papers published in top journal. Epecially, If I set a voxel threshold of P < 0.001 (with FWHM=4mm and brainmask_05_61*73*61), the threshold of the number of clusters was only 6! I am not sure if it was right, but if so, the results corrected by Alphasim were not even as strict as that with a voxel threshold of P < 0.001 and cluters > 10 (which was refered to as uncorrection in some papers). I wonder if my understanding about Alphasim correction is right?

In addition, I found there was another correction available in REST: GRF correction, which was used in some papers published in top journal (eg., Di Martino et al., 2009). In these papers, authors stated that they used GRF correction with voxel-wise: minimum z score >2.3 and cluster significance: P < 0.05, which was a little defferent from that in REST. According to http://restfmri.net/forum/node/1434, is it equal to voxel level P < 0.017 and cluster level P < 0.05? And if the steps are as follows: selet underlay and overlay---Misc---GRF correction---select brainmask_05_61*73*61---fill out Ps of voxel level and cluster level--- select one tailed---click show it?

Finally, I want to know the order of these three corrections (FDR, Alphasim, and GRF) according to strictness.

Thank you for reading so long post!

Best,

Vincent

YAN Chao-Gan

Mon, 08/18/2014 - 16:51

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## Hi Vincent,

Hi Vincent,

Please have a look on http://rfmri.org/Course section V or section 八. DPABI is specifically dealing with this multiple comparison issue.

It's not correct to use AlphaSim in such a way (using preprocessing smooth kernel), including my first paper (Yan et al., 2009).

The correct way is using the estimated smoothness. "Smoothness estimation based on the 4D residual is built in regression function – smoothness is written to the NIfTI headers automatically. For AlphaSim and GRF multiple comparison correction, only using smooth kernel applied in preprocessing is NOT sufficient, please use the estimated smoothness instead."

That's correct, one tailed P: P < 0.017 and cluster level P < 0.05. And corresponds to two tailed P: P < 0.0214 and cluster level P < 0.1.

Strictness is a tricky term, it should depend on data. You can write a post on how these appears on your data.

Best,

Chao-Gan

yaosir

Tue, 08/19/2014 - 01:14

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## Dear Dr. Yan,

Dear Dr. Yan,

Thank you for your helpful reply. I have estimated smoothness instead through REST utilities---REST Alphasim, and the AlphaSimtext was as follows:

Mask filename = BrainMask_05_61x73x61

yaosir

Wed, 08/20/2014 - 02:21

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## I found I was wrong, the

I found I was wrong, the culster size was 52 in this case. The criterion was much more stringent now.