title: A Bayesian framework for estimating the incremental value of a diagnostic test in the absence of a gold standard.
abstract: BACKGROUND
  The absence of a gold standard, i.e., a diagnostic reference standard having perfect sensitivity and specificity, is a common problem in clinical practice and in diagnostic research studies. There is a need for methods to estimate the incremental value of a new, imperfect test in this context.
  
  
  METHODS
  We use a Bayesian approach to estimate the probability of the unknown disease status via a latent class model and extend two commonly-used measures of incremental value based on predictive values [difference in the area under the ROC curve (AUC) and integrated discrimination improvement (IDI)] to the context where no gold standard exists. The methods are illustrated using simulated data and applied to the problem of estimating the incremental value of a novel interferon-gamma release assay (IGRA) over the tuberculin skin test (TST) for latent tuberculosis (TB) screening. We also show how to estimate the incremental value of IGRAs when decisions are based on observed test results rather than predictive values.
  
  
  RESULTS
  We showed that the incremental value is greatest when both sensitivity and specificity of the new test are better and that conditional dependence between the tests reduces the incremental value. The incremental value of the IGRA depends on the sensitivity and specificity of the TST, as well as the prevalence of latent TB, and may thus vary in different populations.
  
  
  CONCLUSIONS
  Even in the absence of a gold standard, incremental value statistics may be estimated and can aid decisions about the practical value of a new diagnostic test.
authors.forename: Daphne I
authors.initials: DI
authors.lastname: Ling
authors.forename: Madhukar
authors.initials: M
authors.lastname: Pai
authors.forename: Ian
authors.initials: I
authors.lastname: Schiller
authors.affiliation: Department of Epidemiology and Biostatistics, McGill University, 1020 Pine Ave West, Montreal H3A 1A2, QC, Canada. nandini.dendukuri@mcgill.ca.
authors.forename: Nandini
authors.initials: N
authors.lastname: Dendukuri
mesh_terms: D001499:Bayes Theorem; D003955:Diagnostic Tests, Routine / Q000379:methods; D006801:Humans; D007371:Interferon-gamma / Q000378:metabolism*; D059425:Interferon-gamma Release Tests / Q000379:methods*; D055985:Latent Tuberculosis / Q000175:diagnosis*; D015233:Models, Statistical; D012372:ROC Curve; D012015:Reference Standards; D012016:Reference Values; D012680:Sensitivity and Specificity; D014374:Tuberculin Test / Q000379:methods*
chemical_list: D007371:Interferon-gamma