| 
      TCEs=treatment change episodes. VL=viral load. NRTI=nucleoside reverse
    transcriptase inhibitor. NNRT=non-nucleoside reverse transcriptase inhibitor.
    PI=protease inhibitor
        |  | Training    set | Test    set |  
        | TCEs | 7,263 | 375 |  
        | Mean (median) baseline VL (log10 c/mL) | 4.20    (4.11) | 4.34 (4.30) |  
        | Mean (median)    baseline CD4(cells/μL) | 269    (230) | 277    (235) |  
        | Treatment History |  |  |  
        | Mean (median) number of previous drugs | 5.82    (5) | 5.56 (5) |  
        | NRTI experience | 99% | 100% |  
        | NNRTI experience | 65% | 54% |  
        | PI experience | 75% | 79% |  
        | Enfuvirtide    experience | 6% | 0% |  
        | Raltegravir    experience | 1% | 1% |  
        | Mean (median) resistance mutations | 8.48 (6) | 8.34 (8) |  
        | Responders(<1.7log10 c/mLfollow-up VL) | 2,550 (35%) | 18 (5%) |  
        | Failures(≥1.7log10 c/mLfollow-up VL) | 4,713 (65%) | 357 (95%) |  |