Things They Should Study: next-of-kin overruling organ donor wishes

I blogged previously that they should change the rules of organ donation so they don't require next-of-kin consent when they already have clear consent from the prospective donor.

I think this would be interesting to study. In what percentage of cases does the next-of-kin not go along with the prospective donor's clearly-expressed wishes? In what percentage of cases does the next-of-kin block donation, and in what percentage do they consent to donation even though the prospective donor doesn't?

(I also wonder, purely as a matter of theoretical ethics, whether there's an ethical difference between consenting to donation against the donor's will (and thereby helping other people) and blocking donation (thereby preventing the donor from helping others). I can make arguments both ways.)