Dear ladies and gentlemen
My name is Dr. Alex Drzezga from Munich in Germany, maybe anybody can
answer my obviously relatively simple question regarding SPM99
correlation analysis in our study in 20 subjects. F-18 FDG scans were
performed at two points of time (baseline and after one year). I want to
do a correlation analysis between metabolic changes within one year and
STABLE covariates (genetic factors, family history).
What would be the proper approach for this type analysis? I tried
"multi-subject with conditions and covariates" and used TWO conditions
and ONE covariate, however the program always demands covariates for
every condition. Therefore I entered the same covariate twice for each
subject at condition 1 and 2 (genetic factors do not change within one
year). My idea was to enter the following contrasts 1 -1 1 1 and 1 -1 -
1 -1 to find out positive or negative correlation between genetic
predisposition and changes of cerebral metabolism, which did not work.
The program only allows 1 -1 1 -1 or 1 -1 -1 1 which would calculate the
correlation of changes in cerebral metabolism with changes in the
covariate, however I want to calculate changes in cerebral metabolism in
dependency of a STABLE covariate only variing between individuals but
not between conditions. Other points that confuse me are: 1. should I
choose covariate interaction with subjects, with conditions or none, and
2. should I calculate a mean around subject means or condition means or
none ?
I would be very thankful for any support !
A. Drzezga
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