title: The indication area of a diagnostic test. Part II--the impact of test dependence, physician's decision strategy, and patient's utility.
abstract: OBJECTIVE
  Any diagnostic test has an indication area of prior probabilities wherein the gain in diagnostic certainty outweighs its loss. Here, we investigate whether indication area and the maximum diagnostic gain are robust measures if we assume test dependence, alternative physician's heuristics, and varying patient's utilities.
  
  
  METHODS
  Three mathematical functions for the dependence of test sensitivity (Se) and specificity (Sp) on the prior disease probability were studied. In addition, three different decision heuristics for further management were explored for the case that "no test" would be done. Finally, the valuation of test outcomes was varied. A sensitivity analysis was performed to determine the impact of the alternative assumptions on the indication area and maximum diagnostic gain.
  
  
  RESULTS
  By assuming test dependence, the indication area shifts to higher priors and increases the maximum diagnostic gain. Decision strategies assuming a "threshold before treat" can inadvertently widen the indication area and increase the maximum diagnostic gain. Varying patient utilities will usually reduce the net diagnostic gain. A sensitivity analysis revealed the robustness of the model.
  
  
  CONCLUSIONS
  The indication area and the maximum diagnostic gain are robust measures of test performance and are easier to interpret than the classical performance measures.
authors.affiliation: Department of Radiotherapy, Academic Medical Center (AMC)-University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands. Electronic address: l.stalpers@amc.nl.
authors.forename: Lukas J A
authors.initials: LJ
authors.lastname: Stalpers
authors.affiliation: Department of Epidemiology, University of Maastricht, Peter Debyeplein 1, 6229 HA Maastricht, The Netherlands.
authors.forename: Patty J
authors.initials: PJ
authors.lastname: Nelemans
authors.affiliation: Radboud Institute for Health Sciences, Radboud University Medical Center, Geert Grooteplein 21, 6525 EZ Nijmegen, The Netherlands.
authors.forename: Sandra M E
authors.initials: SM
authors.lastname: Geurts
authors.affiliation: Department of Radiotherapy, Academic Medical Center (AMC)-University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands.
authors.forename: Erik
authors.initials: E
authors.lastname: Jansen
authors.affiliation: Department of Radiotherapy, Academic Medical Center (AMC)-University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands.
authors.forename: Peter
authors.initials: P
authors.lastname: de Boer
authors.affiliation: Radboud Institute for Health Sciences, Radboud University Medical Center, Geert Grooteplein 21, 6525 EZ Nijmegen, The Netherlands.
authors.forename: André L M
authors.initials: AL
authors.lastname: Verbeek
mesh_terms: D000465:Algorithms; D003955:Diagnostic Tests, Routine; D006801:Humans; D008962:Models, Theoretical; D011336:Probability; D012680:Sensitivity and Specificity
keywords: Diagnostic gain; Indication area; Patient utility; Physician heuristics; Posterior test probability; Prior test probability