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You stated that you have a contrast between two conditions. This implied that you have one measurement per subject. Thus, the two-sample t-test would be appropriate.

If you mean that you have two conditions that you want to compare between groups, then you have 2 measures per subject. Thus, the flexible factorial would be appropriate. Remember that you will only be able to compare the two conditions or the group*condition interaction. The effect of group is invalid.

Best Regards, Donald McLaren
=================
D.G. McLaren, Ph.D.
Postdoctoral Research Fellow, GRECC, Bedford VA
Research Fellow, Department of Neurology, Massachusetts General Hospital and
Harvard Medical School
Website: http://www.martinos.org/~mclaren
Office: (773) 406-2464
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On Mon, May 7, 2012 at 6:39 PM, Mike Sugarman <[log in to unmask]> wrote:
From my understanding, a two-sample t-test is for the comparison of a single condition across groups. I have a contrast between two conditions that I would like to compare between groups. Would the appropriate design for such a comparison involve the inclusion of an interaction effect between condition and group? And would a flexible factorial be the most appropriate method for this comparison?