Biomedical Engineering Reference
In-Depth Information
associated with a worse overall prognosis, with more frequent disease-related
complications and a higher risk of mortality. Once a patient's viral load sur-
passes a predetermined threshold, this patient is said to have experienced
virological failure. The time to virological failure can be perceived as an ob-
jective, individual-specific landmark of disease progression. Persistently high
HIV viral loads in the setting of antiretroviral medication treatment signify
nonadherence, drug resistance, or an ineffective drug regimen. Therefore, HIV
viral loads can be used to clinically gauge the relative effectiveness of an an-
tiretroviral regimen in an HIV-positive individual.
Because patients may have died before ever experiencing virological fail-
ure, the composite outcome defined as time until either virological failure or
death is often more suitable because it is well-defined for all study participants
and can be used as an equally valid measure of treatment effectiveness. For
example, it precludes hypothetical situations wherein a highly toxic treatment
may be wrongly perceived as beneficial in delaying virological failure simply
because it has prematurely resulted in the death of the sickest patients before
the latter could experience virological failure. Participants in the study may
have experienced any of three patterns of events on the outcome of interest,
as listed below.
1. The participant may have developed virological failure within the study
time frame. In this case, it is known that virological failure preceded
death. The exact time until virological failure, however, is not known
exactly but instead found to lie in some time interval, because viral loads
were obtained at bimonthly visits. The composite outcome of interest is
therefore interval-censored.
2. The participant may have died before virological failure has been ob-
served. In this case, it is generally unknown which of death and virolog-
ical failure occurred first, although the composite outcome is known to
have taken place no earlier than the last study monitoring time before
 
Search WWH ::




Custom Search