I have gone through a few literature to understand family-based association study and population based case-control study. I know family based association study is where we have in-family cases and controls samples and population based case-control study is where we have unrelated samples from the same ethnic group. However, I am still finding it difficult to understand specifically under which circumstances we use one over the other (is it just when the samples are related vs non-related?). Could someone please explain me the major differences of these to study in a few points like you would to a fifth grader. Thanks.