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Subject:

design help

From:

Paige Scalf <[log in to unmask]>

Reply-To:

FSL - FMRIB's Software Library <[log in to unmask]>

Date:

Tue, 27 Jan 2004 11:28:19 -0600

Content-Type:

TEXT/PLAIN

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 TEXT/PLAIN (60 lines)
 ```Hi FSL Guru's         I've painted myself into a really complicated repeated measures,         nested design, and I'd appreciate some feedback about whether the         EV's and contrasts I've set up for my second level analysis are         correct.         This is a dual-task task visual attention study, so we have each         of the dual task conditions in a single task form. Because we         have some repeated measures within the dual task condition,         however, we end up with an unbalanced (nested design).         The conditions are         A (single task)                 1 center task                 2 peripheral vision task, proximal to fixation                 3 peripheral vision task, distal to fixation         B (dual task)                 1 center task + proximal peripheral task                 2 center task + distal peripheral task         I've set up my matrix using dummy variables, such that         X1 = 1 single, 0 else         X2 = 1 center single, 0 else         X3 = 1 proximal peripheral single, 0 else         X4 = 1 proximal dual single, 0 else         X5 = subject 1         X6 = subject 2         X7 = subject 3         The EV Matrix ends up being         A1 1 1 0 0 1 0 0         A2 1 0 1 0 1 0 0         A3 1 0 0 0 1 0 0         A4 0 0 0 1 1 0 0         A5 0 0 0 0 1 0 0         And my contrasts are structured         single task 1 0 0 0 0 0 0         dual task 0 0 0 .5 .165 .165 .165         center single 0 1 0 0 0 0 0         etc.         My biggest concern is that my EV's are set up using a very simple         "on/off" matrix, but if I set it up in the more traditional manner         (i.e. 1 for single task, -1 for dual task) I find I can't make the         maths work out for the contrasts I need. (I'll be happy to accept         feedback about any errors, however).         Thanks in advance for any help you can give.         Paige ```

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