title: Assessing the performance of a computer-based policy model of HIV and AIDS.
abstract: BACKGROUND
  Model-based analyses, conducted within a decision analytic framework, provide a systematic way to combine information about the natural history of disease and effectiveness of clinical management strategies with demographic and epidemiological characteristics of the population. Among the challenges with disease-specific modeling include the need to identify influential assumptions and to assess the face validity and internal consistency of the model.
  
  
  RESULTS
  We describe a series of exercises involved in adapting a computer-based simulation model of HIV disease to the Women's Interagency HIV Study (WIHS) cohort and assess model performance as we re-parameterized the model to address policy questions in the U.S. relevant to HIV-infected women using data from the WIHS. Empiric calibration targets included 24-month survival curves stratified by treatment status and CD4 cell count. The most influential assumptions in untreated women included chronic HIV-associated mortality following an opportunistic infection, and in treated women, the 'clinical effectiveness' of HAART and the ability of HAART to prevent HIV complications independent of virologic suppression. Good-fitting parameter sets required reductions in the clinical effectiveness of 1st and 2nd line HAART and improvements in 3rd and 4th line regimens. Projected rates of treatment regimen switching using the calibrated cohort-specific model closely approximated independent analyses published using data from the WIHS.
  
  
  CONCLUSIONS
  The model demonstrated good internal consistency and face validity, and supported cohort heterogeneities that have been reported in the literature. Iterative assessment of model performance can provide information about the relative influence of uncertain assumptions and provide insight into heterogeneities within and between cohorts. Description of calibration exercises can enhance the transparency of disease-specific models.
authors.affiliation: Harvard Medical School, Department of Medicine, Brigham and Women’s Hospital, Boston, Massachusetts, United States of America.
authors.forename: Chara E
authors.initials: CE
authors.lastname: Rydzak
authors.forename: Kara L
authors.initials: KL
authors.lastname: Cotich
authors.forename: Paul E
authors.initials: PE
authors.lastname: Sax
authors.forename: Heather E
authors.initials: HE
authors.lastname: Hsu
authors.forename: Bingxia
authors.initials: B
authors.lastname: Wang
authors.forename: Elena
authors.initials: E
authors.lastname: Losina
authors.forename: Kenneth A
authors.initials: KA
authors.lastname: Freedberg
authors.forename: Milton C
authors.initials: MC
authors.lastname: Weinstein
authors.forename: Sue J
authors.initials: SJ
authors.lastname: Goldie
mesh_terms: D000163:Acquired Immunodeficiency Syndrome / Q000188:drug therapy* / Q000276:immunology / Q000401:mortality / Q000821:virology; D019380:Anti-HIV Agents / Q000627:therapeutic use; D023241:Antiretroviral Therapy, Highly Active; D018791:CD4 Lymphocyte Count; D015331:Cohort Studies; D003198:Computer Simulation; D005260:Female; D006678:HIV / Q000276:immunology / Q000502:physiology; D015658:HIV Infections; D006801:Humans; D008297:Male; D015397:Program Evaluation; D011640:Public Policy; D016896:Treatment Outcome; D014481:United States
chemical_list: D019380:Anti-HIV Agents