title: A comparison of biomarker based incidence estimators.
abstract: BACKGROUND
  Cross-sectional surveys utilizing biomarkers that test for recent infection provide a convenient and cost effective way to estimate HIV incidence. In particular, the BED assay has been developed for this purpose. Controversy surrounding the way in which false positive results from the biomarker should be handled has lead to a number of different estimators that account for imperfect specificity. We compare the estimators proposed by McDougal et al., Hargrove et al. and McWalter & Welte.
  
  
  RESULTS
  The three estimators are analyzed and compared. An identity showing a relationship between the calibration parameters in the McDougal methodology is shown. When the three estimators are tested under a steady state epidemic, which includes individuals who fail to progress on the biomarker, only the McWalter/Welte method recovers an unbiased result.
  
  
  CONCLUSIONS
  Our analysis shows that the McDougal estimator can be reduced to a formula that only requires calibration of a mean window period and a long-term specificity. This allows simpler calibration techniques to be used and shows that all three estimators can be expressed using the same set of parameters. The McWalter/Welte method is applicable under the least restrictive assumptions and is the least prone to bias of the methods reviewed.
authors.affiliation: School of Computational and Applied Mathematics, University of the Witwatersrand, Johannesburg, South Africa. mcwalter@cam.wits.ac.za
authors.forename: Thomas A
authors.initials: TA
authors.lastname: McWalter
authors.forename: Alex
authors.initials: A
authors.lastname: Welte
mesh_terms: D015492:AIDS Serodiagnosis / Q000379:methods* / Q000592:standards; D015415:Biomarkers / Q000378:metabolism*; D002138:Calibration; D003430:Cross-Sectional Studies; D005189:False Positive Reactions; D015658:HIV Infections / Q000097:blood* / Q000453:epidemiology*; D006801:Humans; D015994:Incidence; D015233:Models, Statistical; D008962:Models, Theoretical; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D015415:Biomarkers