For reasons I won't go into, I want to test for group differences between an entire sample A ($n=65$) and a subsample B ($n=45$). All of the variables I want use for mean comparisons are continuous.
Is there an appropriate test for this?
This doesn't seem to meet the sample independence condition for the t-test or Mann-Whitney U. Is it better to just test for group differences using a t-test between B (n=45) and !B (n=20)?