I was wondering if someone can give me a clear understanding on the difference between exchangeable working correlation matrix and unstructured working correlation matrix and when is best to use one or the other?
I'm currently playing which my data and am unsure about the statistical test to use.
I have MRI data from 25 patients. I have 4 (predetermined) lesion types and a control area from which I obtained MRI values. Not all patients have all lesion types, some patients have several of the...