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Dear group Does anymone know the answer to the below repost. I would be grateful for any help. I am unable to move forward in my data analysis without it The questions below are basic question about spm is handling the standard error term in this analysis with various contrasts and scaling of needed for behavioral measures entered into this analaysis. see below Sincerely, Jeff Lorberbaum ---------- Forwarded message ---------- Date: Thu, 3 Feb 2005 08:51:31 -0500 (EST) From: Jeffrey P Lorberbaum <[log in to unmask]> To: [log in to unmask] Subject: multiple regression analysis Dear SPM list and Will Penny: I have a 40 subject mothers listening to infant cries experiment. On each subject, I have contrast images for fMRI activity during a mother's own infant's cry minus its just preceeding rest baseline (Own cry contrast) and a standard (other) infant cry minus its just preceeding rest (Other cry contrast). I have both breast and bottlefeeders and mulitiparous and first-time mothers. Bottlefeeders as its turns out are less educated than breastfeeders. Multiparous mothers are slightly older than first-time mothers. I am interested in the effects of parity, breastfeeding status, as well as their interaction on the fMRI signal and want to adjust out the age and education effects (effects of no interest). I have setup a multiple regression analysis for own and standard cries contrasts separately (I was not sure if this was necessary but it was easier to think about for an initial analysis) Here is the one I set up for own cry. I took the scans for own cry minus rest for each of the 40 moms. (1) column 1 = covariate has 1's for brestfeeding, first time moms; 0's elsewhere (2) column 2 = 1's for brestfeeding, multiparous moms and 0's elsewhere (3) column 3 = covarite has 1's for nonbrestfeeding, first time moms; 0's elsewhere (4) column 4 = 1's for nonbrestfeeding, multiparous moms and 0's elsewhere (5) column 5= age of mother (6) education level of mother My question are: (1) How is spm handling error terms for a contrast such column 1 minus column 2 versus a different contrast such as column 3 versus 4--> is it always the same variance / residual being used or is the adjustment for individual columns variances hidden in the code. (2) Is a contrast such as looking at a t-test in this model of column 1 only (1 then all 0 ) valid if I wanted to know brain effects in breast feeding first time moms only (3) If I wanted to look at effects of age on brain signal (column 5), how is spm handling the error term as the beta coefficient would have a much different value than that of say the ones and zeros in columns 1 to 4. This is of interest because if the same error term is used for each column or contrast then I would have to scale this column in order to get it in range of the others (4) Do I need to orthogonalize or mean center the covariates? (5) Do I need extra columns to account for age and education differing in the 4 groups of the first 4 columns Thank you for any help. Sincerely, Jeffrey Lorberbaum, MD