title: Understanding diagnostic tests 3: Receiver operating characteristic curves.
abstract: The results of many clinical tests are quantitative and are provided on a continuous scale. To help decide the presence or absence of disease, a cut-off point for 'normal' or 'abnormal' is chosen. The sensitivity and specificity of a test vary according to the level that is chosen as the cut-off point. The receiver operating characteristic (ROC) curve, a graphical technique for describing and comparing the accuracy of diagnostic tests, is obtained by plotting the sensitivity of a test on the y axis against 1-specificity on the x axis. Two methods commonly used to establish the optimal cut-off point include the point on the ROC curve closest to (0, 1) and the Youden index. The area under the ROC curve provides a measure of the overall performance of a diagnostic test. In this paper, the author explains how the ROC curve can be used to select optimal cut-off points for a test result, to assess the diagnostic accuracy of a test, and to compare the usefulness of tests.
  
  
  CONCLUSIONS
  The ROC curve is obtained by calculating the sensitivity and specificity of a test at every possible cut-off point, and plotting sensitivity against 1-specificity. The curve may be used to select optimal cut-off values for a test result, to assess the diagnostic accuracy of a test, and to compare the usefulness of different tests.
authors: Department of Paediatric Gastroenterology, Central Manchester and Manchester Children's University Hospitals, Booth Hall Children's Hospital, Manchester, UK. tony.akobeng@cmmc.nhs.uk
authors: Anthony K
authors: AK
authors: Akobeng
mesh_terms: D002097:C-Reactive Protein / Q000032:analysis; D002116:Calcitonin / Q000097:blood; D006801:Humans; D007958:Leukocyte Count; D011498:Protein Precursors / Q000097:blood; D012372:ROC Curve; D012680:Sensitivity and Specificity; D012772:Shock, Septic / Q000175:diagnosis
chemical_list: D011498:Protein Precursors; D002116:Calcitonin; D002097:C-Reactive Protein