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how does a random-effect map of a single group calculated as difference from 0 in a one-sample t-test in 3dttest differ conceptually from the "mean" sub-brick of that same group in a 2dAnova of three patient groups? Would the t-stat subbrik of "mean" in 3dAnova be an apples-to-apples comparison between unequal sample sizes?
Most of the time the difference should be small. If the difference is significant, that indicates some big within-group variation across groups. The output from option "-mean" in 3dANOVA is essentially based on the weighted variance across groups regardless of sample size being equal or not, and the same approach is adopted in two-sample t test with 3dttest. And the weights are proportional to the sample size.
Gang