[Ahmed-USMLE]

1- Detection bias is just like measurement bias in which your focus erronously points to a statistical difference while in fact it should not. Ascertainment bias is the specific detection bias of having the experimenter giving undue efforts to find an effects that he expects to happen.

2- Longitudinal studies follow a group of people who have certain risk or disease and see what happens with them over time. while prospective studies applies an intervention such as adding a risk or treatment and then see what happens over time.

 

[Ahmed-USMLE]

Do they asked you directly on the USMLE what is the difference between this and that study and what books do you recommend i use for Bio statistics really need to know for a long time now

Oh yes they sure do ask such kind of questions
In my exam I remember I got many of them
By the way, not only Step 1 but also Step 2 CK and Step 3