The threshold nature of R 0 is used to monitor and control severe real-time epidemics; control measures are often concluded if R 0 < 1 [48] , making the problems with R 0 more than just theoretical. Due to the inconsistencies in calculation, different diseases cannot be compared unless the same method was used to calculate R 0 ; if HIV has an R 0 of 3 and swine flu has an R 0 of 4, we cannot conclude that swine flu is worse than HIV if different methods were used to determine these values. All we can conclude is that both diseases have R 0 > 1; however, as we have demonstrated, this does not necessarily guarantee disease persistence.