1.) Why do you need a 2-way ANOVA? The order of the 1st level regressors is 1=pre hrf, 2=pre temporal derivative(TD), 2=post hrf, 4=post TD. So, [1 0 -1 0] tests hrf and [0 1 0 -1] tests TD. If so, you get two con images. Why would you need a 2-way ANOVA for this? Isn't it a oneway within-subjects ANOVA with 2 levels?
2.) Is it true that the 1st level t-contrasts test only for greater activations before than after (ie pre minus post)? If one wanted to test both tails (ie pre>post or post>pre), would it be correct to run F contrasts on the first level and take these to the second level?
Best,
Stefan
Mirta -
Simply create T-contrasts for [1 0 -1 0] (canonical: before - after) and [0 1 0 -1]
(derivative: before - after) and enter the resulting contrast images into a (two-way)
ANOVA (no constant term; no within subject effects), and evaluate the F-contrast
for the effects of interest.
Rik
----- Original Message -----
From: "Mirta Villarreal" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, December 15, 2004 7:08 PM
Subject: [SPM] 2nd level analysis with F test?
Hi all
I want to perform a pair-t-test within a group of subjects before and after some
treatment. The problem is that for the individual analysis I get better results when I see
at the [1 0, 0 1] F contrast (model = hrf + first derivative).
In previous e-mails I was recomend to evaluate the T-contrasts [1 0] and [0 1] at the
individual level first and take them to an ANova model. I did it and it was ok.
But how can I take this two contrast for each group to a pair t-test? I should choose 4
pairs? (pair 1= hrf before tretment, pair 2= TD before, pair 3= hrf after, pair 4= TD
after) or I can use directly the [1 0, 0 1] F contrast and 2 pairs?
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