title: Cross-cohort heterogeneity encountered while validating a model for HIV disease progression among antiretroviral initiators.
abstract: OBJECTIVE
  To evaluate a model for predicting time to AIDS or death among HIV-infected persons initiating highly active antiretroviral therapy (HAART).
  
  
  METHODS
  The model was constructed from 1,891 HAART initiators in the Collaborations in HIV Outcomes Research/US (CHORUS) cohort. The model's predictive ability was assessed using internal bootstrap validation techniques and data from 716 HAART initiators at Johns Hopkins HIV Clinical Cohort (JHHCC) in whom HIV disease was, in general, more advanced.
  
  
  RESULTS
  The estimated concordance statistic was 0.632 with the bootstrap method and 0.625 in JHHCC. Mean predicted and observed 3-year AIDS-free survival for JHHCC was 0.76 and 0.73 (95% confidence interval [CI], 0.69-0.77), respectively; mean predicted and observed 5-year AIDS-free survival was 0.69 and 0.57 (95% CI, 0.52-0.62), respectively. Sensitivity analyses showed that the discrepancy between predicted and observed AIDS-free survival after 3 years could be due to differences in lost-to-follow-up rates between cohorts.
  
  
  CONCLUSIONS
  The model was fair at using baseline characteristics to order patients' risk of disease progression, but did not accurately predict AIDS-free survival >3 years after HAART initiation. Different variable definitions, patient characteristics, and loss to follow-up highlight the challenges of using data from one cohort to predict AIDS-free survival in an independent cohort.
authors.affiliation: Department of Biostatistics, Vanderbilt University School of Medicine, Nashville, TN 37232-2158, USA. bryan.shepherd@vanderbilt.edu
authors.forename: Bryan E
authors.initials: BE
authors.lastname: Shepherd
authors.forename: Timothy R
authors.initials: TR
authors.lastname: Sterling
authors.forename: Richard D
authors.initials: RD
authors.lastname: Moore
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Raffanti
authors.forename: Todd
authors.initials: T
authors.lastname: Hulgan
mesh_terms: D000328:Adult; D019380:Anti-HIV Agents / Q000627:therapeutic use*; D023241:Antiretroviral Therapy, Highly Active; D018791:CD4 Lymphocyte Count; D018450:Disease Progression; D004812:Epidemiologic Methods; D005260:Female; D015658:HIV Infections / Q000188:drug therapy* / Q000276:immunology / Q000821:virology; D015497:HIV-1 / Q000302:isolation & purification*; D006801:Humans; D008297:Male; D010349:Patient Compliance; D011379:Prognosis; D016896:Treatment Outcome; D019562:Viral Load
chemical_list: D019380:Anti-HIV Agents