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Hi Tim, Please see below: On 12 February 2016 at 05:29, Timothy W. <[log in to unmask]> wrote: > Hi Anderson, > > Thanks again for your reply! Could you explain how A, B, C, and D in your > design corresponds to these 4 within-subjects scan conditions: Exp_pre, > Exp_post, Control_pre, Control_post? > > In the first design that you sent, I understood them as A=Exp_pre, > B=Exp_post, C=Control_pre, D=Control_post. However, in the second design, > I'm not so sure. > Yes, this is the same for both designs. > > Our main research question is whether (Exp_post - Exp_pre ) > > (Control_post - Control_pre), This can be tested in the 2nd design directly: as you wrote, this is testing (B-A)-(D-C) > 0. The contrasts marked with * can be used to construct this one, and it will then be, for the for the first group: B-A: -2 -1 -1 0 0 0 0 0 ... D-C: 0 1 -1 0 0 0 0 0 ... (B-A)-(D-C): -2 -2 0 0 0 0 0 0 ... Repeating for the 2nd group gives: (B-A)-(D-C): 0 0 0 -2 -2 0 0 0 ... Since you want the difference between groups, then the final contrast is: -2 -2 0 2 2 0 0 0 ... The signs can be reversed to test the opposite. This contrast, however, is already there, in the second design (3-way interaction). It is the same because: (A+D)-(B+C) = -[(B-A)-(D-C)] That is, both ways lead to the same three way interactions. > and whether there's a 3-way interaction with age group. The two hypotheses, that is, (Exp_post - Exp_pre ) > (Control_post - Control_pre) and 3-way interaction with age group are actually the same as shown above. > Perhaps that's what your design is testing, but I could use some > clarification! > Hope this helps. All the best, Anderson > > I appreciate your help, > Tim > > > On Thu, 11 Feb 2016 09:47:44 +0000, Anderson M. Winkler < > [log in to unmask]> wrote: > > >Hi Tim, > > > >Then the design is different. Please have a look here: > > > https://dl.dropboxusercontent.com/u/2785709/outbox/mailinglist/design_tim2.ods > > > >The A, B, C and D represent the 4 conditions organised in a contingency > >table. The interaction is the cross-difference between rows and columns > >(A+D)-(B+C). > > > >All the best, > > > >Anderson > > > > > >On 10 February 2016 at 20:24, Timothy W. <[log in to unmask]> wrote: > > > >> Hi Anderson, > >> > >> Thanks for the quick reply! > >> > >> In our design, we consider subjects as a random effect and condition as > >> fixed. We fixed the conditions before the experiment, and we're > interested > >> in the difference between our fixed levels of pre to post for condition > A > >> vs. condition B (i.e., is the pre-to-post change for condition A > >> significantly different than the pre-to-post change for condition B?). > And > >> then whether or not that interaction is different for the 2 age groups. > >> > >> How would this change the design that you had sketched where condition > was > >> considered as a random effect? > >> > >> > >> Many thanks! > >> > >> Tim > >> > >> > > > > >