I think the answer to the O.P. is....when someone new is signing up as a new member, one of the questions might be, "How did you find this Forum?" or something along those lines....and if a newbie say's, " 'Cuz Walter told me about this place" or something along those lines...that might be a referral. By the way, I'm just totally faking my way through the above answer.
The other question here might be easier to answer, unless I'm wrong or confused, I guess...