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Table 3 Transition probabilities (per three-month period) and data sources

From: The cost-effectiveness of Antiretroviral Treatment in Khayelitsha, South Africa – a primary data analysis

Input parameters Data sources Transition probability (range)
CD4 category at baseline for ART and No-ART
CD4 < 50 cells/ml   0.372 (0.349–0.395)
CD4 50–199 cells/ml   0.628 (0.605–0.651)
Probabilities of transitioning between alive Markov states
First-line regimen to second-line regimen
0–6 months N/A – no patients switched  
6–12 months 0.48% switched by 12 months 0.002 (0.001–0.006)
12–24 months 4.66% switched by 24 months 0.011 (0.007–0.015)
24–36 months 11.73% switched by 36 months 0.019 (0.014–0.026)
36–48 months 15.9% switched by 48 months 0.012 (0.005–0.024)
>48 months Average over 0–48 months 0.011 (0.007–0.017)
No-ART, CD4 50–199 cells/ml to CD4 < 50 cells/ml
all quarters Calculated to ensure 50% surviving at 24 months 0.040 (0.026–0.043)
Probabilities of transitioning to dead Markov states
ART CD4 < 50 cells/ml
0–3 months 86.9% surviving at 3 months 0.131 (0.107–0.159)
3–6 months 83.9% surviving at 6 months 0.034 (0.031–0.038)
ART CD4 50–199 cells/ml
0–3 months 95.9% surviving at 3 months 0.041 (0.030–0.054)
3–6 months 93.9% suriviving at 6 months 0.021 (0.019–0.024)
All patients on ART, irrespective of regimen
6–12 months 86.9% suriviving at 12 months 0.018 (0.017–0.020)
12–24 months 83.4% suriviving at 24 months 0.010 (0.008–0.012)
24–36 months 79.5% surviving at 36 months 0.012 (0.009–0.016)
36–48 months 76.2% suriviving at 48 months 0.010 (0.005–0.017)
>48 months Average over 0–48 months 0.017 (0.013–0.021)
No ART CD4 count < 50 cells/ml
all quarters 20% surviving at 24 months1 0.182 (0.147–0.227)
No ART CD4 50–199 cells/ml
all quarters 50% surviving at 24 months with CD4 < 200 cells/ml2 divided by hazard ratio3 0.039 (0.034–0.043)
  1. 1 No-ART survival with CD4 < 50 cells/μl from Post, Wood et al [52]
  2. 2 No-ART survival with CD4 < 200 cells/μl from Badri, Bekker et al [27]
  3. 3 Hazard ratio for death in CD4 < 50 versus 50–199 cells/μl from Coetzee, Hildebrand et al [26]