It is becoming increasingly difficult to understand the HIV epidemic in industrialized countries. Until the mid-1990s, HIV infections were estimated by calculating backwards from reported AIDS cases according to well-established patterns of disease progression. This method gave a delayed picture of new infections but was useful in ascertaining changes in the overall scale of the epidemic. While AIDS remains fatal, life-prolonging therapy can postpone death for an unknown period of time for some HIV-positive people. This means that the timing of the progression from HIV infection to AIDS and from AIDS to death has become very difficult to predict, so calculating past trends in HIV infection from current AIDS cases or deaths has become more or less impossible.