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I have a two-group pre-test/post-test design with one dependent variable. I want to find out whether or not an intervention has been effective. Would it be more appropriate to do a t-test on the gain scores or a two-way mixed ANOVA?
Thanks!
It's also worth noting that the means of both groups at pre-test were identical.
It doesn't matter. These are the same test. (Try it, you'll get the same p-value, and $F$ will be equal to $t^2$.
However, most people would suggest doing a regression analysis, and controlling for baseline scores. If you don't, you're acting as if pre-and post scores are correlated 1.0 (within groups).
See, for example: http://www.ncbi.nlm.nih.gov/pubmed/16895814
