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Hi I have a couple questions about setting up first level factorial designs and testing for interactions. I have factor P (perspective taking) which has two levels (other, self). I also have factor G (guilt) which has four levels (none, low, med, high). I thought of doing this with two EVs , one for each factor. The factor P can be specified with -1 and 1 for 'other' or 'self' in the three column timing file (-1 and 1). For factor G, I can weight the events as -3, -1, 1, 3 as weights in the 3 column timing file. Then in FEAT I can click on the interaction of EV for factor P and the EV for factor G. Is this a valid set up for this design to assess main effects and interactions ? Also is it valid to weight factor G with 1, 2, 3, 4 (instead of -3, -1, 1, -3)? Alternatively if I collapse the G levels into none+low and med+high resulting in two levels instead of 4, then I could use -1 and 1 in the three column file. In this case what is the difference between using the interaction button in FEAT versus a double contrast (timing file to specfify -1 and 1 at for the two P levels; -1 and 1 for the simplified G levels; and a contrast of the EVs for P and G) ? Finally, as a variant to above, how about creating 4 EVs, guilt, neutral, other, self, and doing the double contrasts at the second level. Is there a difference between this approach and using the interaction approach? In general is there a recommended approach for doing more complicated factorial design interactions of first level inputs ? Raj Morey