1. What Happens to the Performance of a Diagnostic Test when the Disease Prevalence and the Cut-Point Change? Pathological scores Healthy scores Healthy population Sick population Cut-point - + Click on the + or – to shift the cut-point + - Prevalence Click on the + or – to alter the prevalence Remember: PPV = predictive value of a positive test result NPV = predictive value of a negative test

2. Pathological scores Healthy scores Healthy population Sick population Cut-point + + − Prevalence Disease + − + Test − 25 275 82 18 Sensitivity 82/100 82% Specificity 275/300 91.7% PPV 80/107 74.8% NPV 275/295 93.2% 25% −

3. Pathological scores Healthy scores Healthy population Sick population Cut-point + + − Prevalence Disease + − + Test − 20 280 73 27 Sensitivity 73/100 73% Specificity 280/300 93.3% PPV 73/93 78.5% NPV 280/307 91.2% 25% −

4. Pathological scores Healthy scores Healthy population Sick population Cut-point + + − Prevalence Disease + − + Test − 15 285 70 30 Sensitivity 70/100 70% Specificity 285/300 95% PPV 70/85 82.4% NPV 285/315 90.5% 25% −

5. Pathological scores Healthy scores Healthy population Sick population Cut-point + + − Prevalence Disease + − + Test − 10 290 63 37 Sensitivity 63/100 63% Specificity 290/300 96.7% PPV 63/70 86.3% NPV 290/327 88.7% 25% −

6. Pathological scores Healthy scores Healthy population Sick population Cut-point + − Prevalence Disease + − + Test − 0 300 52 48 Sensitivity 52/100 52% Specificity 300/300 100% PPV 52/52 100% NPV 300/348 86.2% 25% −

7. Pathological scores Healthy scores Healthy population Sick population Cut-point + + − Prevalence Disease + − + Test − 45 255 90 10 Sensitivity 90/100 90% Specificity 255/300 85% PPV 90/135 66.7% NPV 255/265 96.2% 25% −

8. Pathological scores Healthy scores Healthy population Sick population Cut-point + + − Prevalence Disease + − + Test − 66 234 95 5 Sensitivity 95/100 95% Specificity 234/300 78% PPV 95/161 59% NPV 234/239 97.9% 25% −

9. Pathological scores Healthy scores Healthy population Sick population Cut-point + + − Prevalence Disease + − + Test − 105 195 100 0 Sensitivity 100/100 100% Specificity 195/300 65% PPV 100/205 48.8% NPV 195/195 100% 25%

10. Pathological scores Healthy scores Healthy population Sick population Cut-point + + Prevalence Disease + − + Test − 42 458 49 11 Sensitivity 49/60 82% Specificity 458/500 91.6% PPV 49/91 53.8% NPV 458/469 97.7% 10% −

11. Pathological scores Healthy scores Healthy population Sick population Cut-point + + Prevalence Disease + − + Test − 33 467 44 16 Sensitivity 44/60 73.3% Specificity 467/500 93.4% PPV 44/77 57.1% NPV 467/483 96.9% 10% −

12. Pathological scores Healthy scores Healthy population Sick population Cut-point + + Prevalence Disease + − + Test − 25 475 42 18 Sensitivity 42/60 70% Specificity 475/500 95% PPV 42/67 62.7% NPV 475/493 96.4% 10% −

13. Pathological scores Healthy scores Healthy population Sick population Cut-point + + Prevalence Disease + − + Test − 15 485 38 22 Sensitivity 38/60 63.3% Specificity 485/500 97% PPV 38/53 71.7% NPV 485/506 95.8% 10% −

14. Pathological scores Healthy scores Healthy population Sick population Cut-point + Prevalence Disease + − + Test − 0 500 31 29 Sensitivity 31/60 51.7% Specificity 500/500 100% PPV 31/31 100% NPV 500/529 94.5% 10% −

15. Pathological scores Healthy scores Healthy population Sick population Cut-point + + Prevalence Disease + − + Test − 75 425 54 6 Sensitivity 54/60 90% Specificity 425/500 85% PPV 54/129 41.9% NPV 425/431 98.6% 10% −

16. Pathological scores Healthy scores Healthy population Sick population Cut-point + + Prevalence Disease + − + Test − 110 390 57 3 Sensitivity 57/60 95% Specificity 390/500 78% PPV 57/167 34.1% NPV 390/393 99.2% 10% −

17. Pathological scores Healthy scores Healthy population Sick population Cut-point + + Prevalence Disease + − + Test − 175 325 60 0 Sensitivity 60/60 100% Specificity 325/500 65% PPV 60/235 25.5% NPV 325/325 100% 10%

18. Pathological scores Healthy scores Healthy population Sick population Cut-point + − Prevalence Disease + − + Test − 8 92 82 18 Sensitivity 82/100 82% Specificity 92/100 92% PPV 82/90 91% NPV 92/110 83.6% 50% −

19. Pathological scores Healthy scores Healthy population Sick population Cut-point + − Prevalence Disease + − + Test − 7 93 73 27 Sensitivity 73/100 73% Specificity 93/100 93% PPV 73/80 91.3% NPV 93/120 77.5% 50% −

20. Pathological scores Healthy scores Healthy population Sick population Cut-point + − Prevalence Disease + − + Test − 5 95 70 30 Sensitivity 70/100 70% Specificity 95/100 95% PPV 70/75 93.3% NPV 95/125 76% 50% −

21. Pathological scores Healthy scores Healthy population Sick population Cut-point + − Prevalence Disease + − + Test − 3 97 63 37 Sensitivity 63/100 63% Specificity 97/100 97% PPV 63/66 95.5% NPV 97/134 72.4% 50% −

22. Pathological scores Healthy scores Healthy population Sick population Cut-point − Prevalence Disease + − + Test − 0 100 52 48 Sensitivity 52/100 52% Specificity 100/100 100% PPV 52/52 100% NPV 100/148 67.6% 50% −

23. Pathological scores Healthy scores Healthy population Sick population Cut-point + − Prevalence Disease + − + Test − 15 85 90 10 Sensitivity 90/100 90% Specificity 85/100 85% PPV 90/105 85.7% NPV 85/95 89.5% 50% −

24. Pathological scores Healthy scores Healthy population Sick population Cut-point + − Prevalence Disease + − + Test − 22 78 95 5 Sensitivity 95/100 95% Specificity 78/100 78% PPV 95/117 81.2% NPV 78/83 94% 50% −

25. Pathological scores Healthy scores Healthy population Sick population Cut-point + − Prevalence Disease + − + Test − 35 65 100 0 Sensitivity 100/100 100% Specificity 65/100 65% PPV 100/135 74% NPV 65/65 100% 50%