help > Help interpreting VLSM NPM permutation results
Nov 19, 2019  05:11 AM | marcelodelboni
Help interpreting VLSM NPM permutation results
Dear all,

We're conducting an exploratory binary images, binary groups VLSM analysis in NPM (2012) with ~60 patients with brain lesions divided into two groups: with a specific clinical deficit (coded as 0 in .val file) and without that deficit / "healthy" group (coded as 1 in the .val file). Only tested voxels damaged in at least 10%, set permutations = 4000, aiming at p<0.05 and run the stats. Could you please give us an advice on how to interpret the results below?

L Range -1.522...4.563
L+ FDR Z 0.050=2.21332455, 0.01=9.20000000
L- FDR Z 0.050=9.20000000, 0.01=9.20000000
L+: permutationFWE , 0.050=-0.00024465, 0.025=-0.00008664, 0.01=-0.00002900
L-: permutationFWE , 0.050=0.00038112, 0.025=0.00017590, 0.01=0.00007933

The FDR corrected results are great; when we display them using the threshold =  2.2133 we have nice results, compatible with current literature.

However, we don't understand the L+ permutation-FWER corrected results.
Why are Z values negative? Since they're negative we thought maybe these show the inverse "correlation" -i.e., brain areas more lesioned in the 1 group ("healthy")? How do we look at areas more lesioned in the 0, deficit group? Should we look at the L- tail? But why would we look at the L+ tail in FDR and the L- tail in permutation-corrected results?

Thanks a lot in advance for your help!
Marcelo

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TitleAuthorDate
Help interpreting VLSM NPM permutation results
marcelodelboni Nov 19, 2019
Chris Rorden Nov 19, 2019