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Hello SPM-users, I would like to re-post a question on FDR multiple test correction and VBM. We have processed n=80 subjects acc. to an optimized VBM protocol including Jacobian modulation and smoothing at FWHM 12 mm. Six multiple regression models have been set up, the main regressor of interest (of each) being a behavioural result (psychological test battery), along with covariates age and gender. (For simpl. I use the term 'activation' for voxels that are significant after applying a directed t-test on the main regressor). At uncorrected p < 0.001 correlation maps show activations well balanced between focal/regional (not too excessive), also reasonable variation between the tests is found. Correction at FDR 0.05 tends to lead to rather excessive activations in most contrasts. Using a more stringent q < 0.005 brings produces areas about comparable with p uncorr 0.001. However, with the FDR being adaptive the effect of the correction differs between contrasts and it seems odd to adapt the FDR threshold for each contrast. So I used the script FDRill to check the T-distribution: for most contrast it is clearly shifted (up to about +2), so a number of questions arise: 1. Is FDR appropriate at all and how could I deal with the adaptiveness of this type of multiple test correction, i. e. is it appropriate to use different q values to different contrasts - which obviously contain results at different 'strength' end extent'? 2. Can results - as earlier suggested - be p resented in the way that uncorrected voxels and clusters are listed at uncorrected p=0.001 but in addition it is checked if clusters survive FDR, and only such clusters are discussed as significant result? 3. The 'ill' T-distribution: I have not modelled total GM volume as covariate because we were also looking for regional (e. g. a whole lobe) effects and thought this would be overcorrected by such a covariate. What possibilites are there to improve this? Any help is appreciated! Thanks very much in advance! Philipp Saemann Max-Planck-Institute of Psychiatry Kraepelinstr. 2-10 80804 Munich Germany