Dear All,
I am trying to run a paired group analysis using an additional covariate and
would like some advice. I apologise if it seems basic, but I am still trying to
get a grip on the analysis.
I have a group who were scanned twice and I want to compare their
performance pre and post, as well as adding a RT covariate.
However, I am using contrasts e.g. happy-neutral (pre) > happy-neutral
(post).
For my additional RT covariate do I have to calculate my mean RT as happy-
neutral for each group?
Also I am a bit confused about how to set up the contrasts to look at
pre>post with covariate. I have read a couple of previous posts and remain
confused.
EV1 =group
EV2-3 = partciapnts (obviously I have more this is merely for example)
EV4= RT covariate
EV1 EV2 EV3 EV4
con1 1 0 0 0
con2 -1 0 0 0
The above should give Pre>post and the post>pre activation. I initailly though
that this will show activation which already includes the additional contrast as
it is defined as EV4, but after reading previous posts I am not sure. Is this not
the case?
If not how would I define the contrast? I thought it would be con3 and con4
EV1 EV2 EV3 EV4
con3 1 0 0 1
con4 -1 0 0 1
con5 0 0 0 1
But reading previous posts contrast 5 was recommeded. I am unclear how this
tells me where my differences are between my groups adding in the additonal
covariate.
I would really appreciate it if someone could explain this to me.
Thanks in advance
Rebecca
|