On Jan 3, 2008 9:41 PM, Heather L. Urry <[log in to unmask]> wrote:
> Hello:
>
> I'm hoping to receive feedback on how to set up a fully within-subjects
> factorial design for 27 subjects. I have two factors, Factor A with levels
> A1 and A2, and Factor B with levels B1, B2, B3, and B4. Each subject
> completed 3 runs (randomized event-related with all conditions represented
> in each run). I'm thinking that the best way to proceed is to model the two
> main effects and the interaction at the first-level for each run (where EVs
> 1 through 8 represent the 2*4 = 8 conditions):
<snippety>
> Input 27 (subj 27)0 0 0.. 1
>
> I've done my best to adapt the examples posted on the website for the
> Multi-Session & Multi-Subject (Repeated Measures - Three Level Analysis).
> Does this plan make sense?
Yes - I think that makes sense.
> As a follow-up, subjects provided a rating after each trial. If I want to
> enter that in the first-level analysis, I need to demean it, but should that
> be demeaned *within* each condition so as not to soak up mean differences
> between conditions?
Correct - demean within condition gives you the effect of rating once
main condition effects have been taken into account. i.e. residual or
orthogonal variance.
Second, should the demeaned values be scaled to a
> maximum of 1?
Not sure of the necessity of that, though it certainly won't hurt.
> Finally, if I'm using a 3 column format text file, would the
> demeaned rating value be entered as the "event", i.e., replacing the
> constant value of 1 that's currently entered in column 3 of my 3 column
> format EVs at the first level?
Yes - that's correct.
-Tom
--
School of Psychology and CLS
University of Reading
3 Earley Gate, Whiteknights
Reading RG6 6AL, UK
Ph. +44 (0)118 378 7530
[log in to unmask]
http://www.personal.reading.ac.uk/~sxs07itj/index.htm
|