Statistical test for sample selection bias

Question

[agatawesol]

Hi,

I am conducting a study on a subset of a cohort: we randomly selected 160 subjects out of 750 in the total cohort. Which statistical test would be the most appropriate to run on the clinical data I have (e.g. age, gender, drug response) to test for any sampling bias?

I was thinking about Mann Whitney test, but one of the assumptions is that the samples are independent of each other.

Thanks in advance!