help > RE: graph theory and nbs
Nov 5, 2022  11:11 PM | Andrew Zalesky
RE: graph theory and nbs
Hi GT,

it is certainly possible for significant effects to be found in nodal metrics but not in connectivity. 

Be sure to correct for multiple comparisons across the set of nodes and measures. So if you have 100 nodes and testing for 3 nodal measures, the total number of comparisons is 300. 

It is difficult to provide meaningful comments without knowing more about your study. 


Originally posted by gthngjy:
Hi Andrew, 

I ran some graph theory analyses prior to using NBS and the results showed case-control differences in quite a few brain regions (mostly cases having lower values, such as lower nodal efficiency, than controls) after controlling for nuisance covariates like age, sex and site. I then tried using NBS to identify subnetworks, with the expectation that I will find significant subnetworks involving the same regions identified in the graph theory analyses. I used a two-sample t-test with the contrast [-1 1 0 0 0] - the first column for cases, second column for controls, third column for age and fourth column for site. However, there were no significant subnetworks over a range of primary thresholds (p<0.001 to p<0.05) for both extent and intensity. I also tried using the FDR option with 50,000 permutations but likewise, no significant differences were found. Significant subnetworks were identified if I do not control for the nuisance covariates but I do think it is necessary to add them in.

I am a bit puzzled by the results because there were differences at the nodal level and it would make sense to see differences at the connection level. What do you think? I know this is not directly related to NBS methodology, but it would be really great if I can get your opinion on this. 

Thank you very much!

Best Regards

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gthngjy Nov 5, 2022
RE: graph theory and nbs
Andrew Zalesky Nov 5, 2022
gthngjy Nov 6, 2022
Andrew Zalesky Nov 7, 2022