Dear SPMers,
We have a 2-groups PET study (9 Healthy(G1) vs 8
Patients(G2)) with 6 conditions (N,H,A,B,C,S) and 2 replications by
condition.
N and H are control conditions for the S activation
condition
A is control condition for B and C activation
condition.
we wanted to compare the two groups for the S-N,
S-H and C-A contrasts.
We first defined individual contrasts and we then
performed second level analyses in order to compare the two groups, i.e.,
S-N(G1) and S-N(G2) interaction; S-H(G1) and S-H(G2) interaction; C-A(G1) and
C-A(G2) interaction. These analyses have very low degrees of freedom
(15). But, since each individual contrast involved in these analyses was
obtained from 4 scans (2conditions, 2 replications), the total number of scans
involved in the analyse is 4 x (9 + 8) = 68.
Is there mean to correct df with the real number of
scans?
Thank you