title: The agreement chart as an alternative to the receiver-operating characteristic curve for diagnostic tests.
abstract: OBJECTIVE
  For diagnostic tests, the most common graphical representation of the information is the receiver-operating characteristic (ROC) curve. The "agreement chart" displays the information of two observers independently classifying the same n items into the same k categories, and can be used if one considers one of the "observers" as the diagnostic test and the other as the known outcome. This study compares the two charts and their ability to visually portray the various relevant summary statistics that assess how good a diagnostic test may be, such as sensitivity, specificity, predictive values, and likelihood ratios.
  
  
  METHODS
  The geometric relationships displayed in the charts are first described. The relationship between the two graphical representations and various summary statistics is illustrated using data from three common epidemiologically relevant health issues: coronary heart disease, screening for breast cancer, and screening for tuberculosis.
  
  
  RESULTS
  Whereas the ROC curve incorporates information on sensitivity and specificity, the agreement chart includes information on the positive and negative predictive values of the diagnostic test.
  
  
  CONCLUSIONS
  The agreement chart should be considered as an alternative visual representation to the ROC for diagnostic tests.
authors.affiliation: University of North Carolina, 137 E. Franklin Street, Chapel Hill, NC 27514, USA. kant@unc.edu
authors.forename: Shrikant I
authors.initials: SI
authors.lastname: Bangdiwala
authors.forename: Ana S
authors.initials: AS
authors.lastname: Haedo
authors.forename: Marcela L
authors.initials: ML
authors.lastname: Natal
authors.forename: Andrés
authors.initials: A
authors.lastname: Villaveces
mesh_terms: D019540:Area Under Curve; D001943:Breast Neoplasms / Q000175:diagnosis* / Q000453:epidemiology; D003327:Coronary Disease / Q000175:diagnosis* / Q000453:epidemiology; D003955:Diagnostic Tests, Routine / Q000379:methods*; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D008403:Mass Screening; D015233:Models, Statistical; D015588:Observer Variation; D012372:ROC Curve; D012680:Sensitivity and Specificity; D014376:Tuberculosis / Q000175:diagnosis* / Q000453:epidemiology