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Dear SPM community, I would very much appreciate comments of experienced SPM statisticians on the following design and analysis: An investigation of two groups was performed using MRI and optimized VBM (n=26). In addition, other data were acquired in both groups. Statistically spoken we investigate the variable gray matter probability in each voxel, with knowledge of the categorial group factor, the continous whole brain volume factor, and the continous other factor. Our first approach was to build a multiple correlation. We chose the simple correlation (regression) model in SPM and loaded a text-file containing the three factors group in three lines. This leads to a SPM matrix with the four rows row 1:group (0 and 1), row 2:whole brain volume (continous), row3:other factor (continous), and row4: error. In the results step, a contrast was defined putting +1 on the other factor (row3). In our opinion this should model the correlation of the other factor with gray matter probability. Is this thought correct? Second there was a discussion about using an ANCOVA model. Definition of the ANCOVA with both groups and the two covariates whole brain volume and other factor leads to a SPM design matrix with five rows. Row 1: group 0, row 2:group 1, row 3: error, row 4: whole brain volume (continous) and row 5: other factor (continous). However we are not sure about the significance of putting a contrast +1 on the other factor (row 5). Does this kind of analysis tell us anything about the relation of the other factor with gray matter probability, and what exactly? Yours Carsten