I need some assitance with the SPM99 statistics section. I have an FDG-PET
study with 2 scans per subject.
I initially chose the paired t-test from Basic Models. I noticed that I was
not
given an option to specify proportional scaling for Global Normalization,
and
the Design diplay indicated that there was no global normalization. I had
entered the following in the model
Global Scaling: mean voxel within per image (full mean/8mask)
Scaling of Grand Mean: 100
I then chose Multi-subject - Coniditons and Covariates. There I was given
an
option for Proportional Scaling for Global Normalization.
I do not understand why proportional scaliing is not an option under paired
t-tests. Is proportional scaling implicit in the paired t-test design ? If
so,
then why does the Design display indicate no proportional scaling. Is the
lack
of proportional scaling also true for the other designs under Basic Models.
I think I need a simple explanation for the relative usage of the PET/SPECT
models vs. Basic Models.
sg
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