Haemophilia is considered the best test of the HIV-AIDS hypothesis by both denialists and AIDS researchers. While Duesberg claims AIDS in haemophiliacs is caused by contaminated clotting factors and HIV is a harmless passenger virus, this result is contradicted by large studies on haemophiliac patients who received contaminated blood. A comparison of groups receiving high, medium and low levels of contaminated clotting factors found the death rates differed significantly depending on HIV status. Of 396 HIV positive haemophiliacs followed between 1985 and 1993, 153 died. The comparative figure for the HIV negative group was one out of 66, despite comparable doses of contaminated clotting factors. A comparison of individuals receiving blood donations also supports the results; in 1994 there were 6888 individuals with AIDS who had their HIV infection traced to blood transfusions. Since the introduction of HIV testing, the number of individuals whose AIDS status can be traced to blood transfusions was only 29 (as of 1994).