6. Developmental characteristics: Cut-points and Receiver Operating Characteristic (ROC) Healthy

7. Developmental characteristics: Cut-points and Receiver Operating Characteristic (ROC) Healthy Sick

8. Developmental characteristics: Cut-points and Receiver Operating Characteristic (ROC) Fals pos= 20% True pos=82%

9. Developmental characteristics: Cut-points and Receiver Operating Characteristic (ROC) Fals pos= 9% True pos=70%

10. Developmental characteristics: Cut-points and Receiver Operating Characteristic (ROC) F pos= 100% T pos=100%

11. Developmental characteristics: Cut-points and Receiver Operating Characteristic (ROC) F pos= 50% T pos=90%

13. Developmental characteristics: Cut-points and Receiver Operating Characteristic (ROC) Receiver Operating Characteristic (ROC)

14. Developmental characteristics: Cut-points and Receiver Operating Characteristic (ROC) Receiver Operating Characteristic (ROC)

17. Clinical Interpretation: Predictive Values Most test positives below are sick. But this is because there are as many sick as healthy people overall. What if fewer people were sick, relative to the healthy?

18. Clinical Interpretation: Predictive Values Now most test positives below are healthy. This is because the number of false positives from the larger healthy group outweighs the true positives from the sick group. Thus, the chance that a test positive is sick depends on the prevalence of the disease in the group tested!

22. Clinical Interpretation: Predictive Values T+ D+ T+ and D+

27. Use This Table ? NO

28. Make a New Table

29. Make a New Table

35. Clinical Interpretation: Positive Likelihood Ratio and PV+ O = PRE-TEST ODDS OF DISEASE POST-ODDS (+) = O x LR+ =

37. Clinical Interpretation: Negative Likelihood Ratio and PV- POST-ODDS (-) = O x LR- =

39. Post test probability given a negative test = Post odds (-)/ 1+ post odds (-)

41. Clinical interpretation of post-test probability Disease ruled out Disease ruled in

45. Using Likelihood Ratios to Determine Post-Test Disease Probability

48. Clinical Interpretation: Predictive Values

49. Clinical Interpretation: Predictive Values

62. If the test is used to decide referral for gold standard? 1000 900 Sp 828/900 = .92 100 Sn95/100 =.95 Total 833 828 5 Test Negative 167 72 95 Test Positive Total No Disease Disease

63. If the test is used to decide referral for gold standard? 1000 900 164 Sp 99/164=.4 100 86 Sn85/86=.99 Total 833 833  100 828 99 5 1 Test Negative 167 167  150 72 65 95 85 Test Positive Total No Disease Disease

64. If the test is used to decide referral for gold standard? 250 164 Sp 99/164=.4 86 Sn85/86=.99 Total 100 99 1 Test Negative 150 65 85 Test Positive Total No Disease Disease