摘要：The aim of this study is to model the progression of HIV/AIDSdisease of an individual patient under ART follow-up using semi-Markov pro-cesses. Recorded hospital data were obtained for a cohort of 710 patients atFelege-Hiwot referral hospital, Ethiopia, who have been under ART follow-up from June 2005 to August 2009. States of the Markov process are de nedby the seriousness of the sickness based on the CD4 counts in cells/microliter.The ve states considered are: state one (CD4 count > 500); state two (350< CD4 count 500); state three (200 < CD4 count 350); state four (CD4count 200); and state ve (Death). The rst four states are named asgood or alive states. The ndings obtained from the current study are asfollows: within the good states, the transition probability from a given stateto the next worse state increases with time, gets optimum at a time andthen decreases with increasing time. This means that there is some periodof time when such probability is highest for a patient to transit to a worsestate of the disease. Moreover, the probability of dying decreases with in-creasing CD4 counts over time. For an HIV/AIDS patient in a speci c stateof the disease, the probability of being in same state decreases over time.Within the good states, the results show that probability of being in a betterstate is non-zero, but less than the probability of being in worse state. Atany time of the process, there is more likely to be in worse state than tobe in better one. The conditional probability of staying in same state untila given number of month decreases with increasing time. The reliabilityanalysis also revealed that the survival probabilities are all declining overtime. This implies that patient conditions should be improved with ART toimprove the survival probability.
