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Dear SPMers, We are running a full factorial model in SPM 8 using a condition variable (representing two groups) and 8 additional covariates, including 1 Condition x Covariate interaction term. We've extracted the data from one voxel to compare results with SPSS linear regression or ANOVA programs, fully expecting them to agree (as a check that our script was working correctly). We find that the beta values estimated by SPM for that voxel for each variable in the model and the regression coefficients estimated by SPSS are in perfect agreement. The residual degrees of freedom in both SPM and SPSS also agree. However, we are finding that the t-test values generated in SPM and SPSS do not agree. For example, for the interaction term of interest, in SPSS t =1.459, but in SPM's t-map t =1.3414. We can't figure out why, but we suspect that the standard error of the beta must be estimated differently (since the betas and the degrees of freedom appear to be the same in SPSS and SPM). Does anyone have any ideas about why we are observing these discrepancies? Any insights or strategies for tracking this down would be greatly appreciated. Thanks, Dan Daniel H. Mathalon, Ph.D., M.D. Professor of Psychiatry University of California, San Francisco Mail Address: Psychiatry Service 116d San Francisco VA Medical Center 4150 Clement St. San Francisco, CA 94121 Office phone: (415) 221-4810, ext. 3860 Fax: (415) 750 6622 e-mail: [log in to unmask]