Dear experts
Apologize for the basic question.
I'm analyzing FDG-PET scans in 25 patients with a neurological disorder.
In addition to group comparison (patients vs controls), I want to correlate regional glucose metabolism with clinical parameter such as disease duration.
I chose 'single subject_covariate only' module in PET models (spm2), with disease duration as covariate-of-interest and age/sex as nuisance variables.
In the next step of 'Select global normalization', there are two options, Ancova vs. proportional scaling. Which one is appropriate for my study?
I have tried each method but the results are very different.
Accodring to an spm99 manual in Website, there is the following sentence, "AnCova is advised for multi-subject studies unless differences in global flow are large (e.g., due to variability in injected tracer dose). Because AnCova also uses one degree of freedom for each subject/group, proportional scaling may be preferable for single-subject studies."
Does the selection of 'Ancova' is more suitable for my design?
Many thanks for the good advice.
Kim
