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Hi, > Only when dividing the ResMS map by the effective df's (SPM.xX.erdf) did I > get a correct estimation of the individual SD, > (for a particular contrast) using: > > SDmap = sqrt ( (resms_map/spm.xX.erdf) * (contrast'*SPM.xX.Bcov*contrast) ); > > > which is based on the formula for t : > > spmT(i) = contrast'*beta(i)/sqrt(ResMS * contrast' * SPM.xX.Bcov * contrast) > > Is one of the creators of SPM2 aware of this (minor) issue? Why do you call > the images ResMS while it appears to be ResSS. I think you just run into this bug: http://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=ind0503&L=SPM&P=R31846&I=-3 As you see, it doesn't affect SPM in its use of the ResMS image, because it uses a stored version of the vol struct, which has the correct scaling... Best, Matthew