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I'm using SPM99 to do parametric analyses of an event-related fMRI experiment. I want to look at factors that predict the magnitude of the BOLD response to individual words e.g. frequency, length. A previous email to the list suggests that SPM can accept multiple parametric modulators: http://www.jiscmail.ac.uk/cgi-bin/wa.exe?A2=ind0102&L=spm&D=0&m=4964&P=25502 However, if I specify more than one parameter of these words and estimate the model, the parametric columns in the design matrix are greyed-out as "not estimable". I guessed that this was because some of the parameters were correlated with each other. I've tried including only columns that are not significantly correlated (by a pearson correlation), but still can't estimate these columns. I've also tried using the matlab "orth" function to orthogonalize the matrix of parameters to no avail. Any suggestions? Matt **************************************************** Matt Davis MRC Cognition and Brain Sciences Unit 15 Chaucer Road, Cambridge, CB2 2EF email: [log in to unmask] tel: 01223 355 294 (#266) NOTE New telephone Fax: 01223 359 062 extension number ****************************************************