1. 1 The probability that a medical test will correctly detect the presence of a certain disease is 98%. The probability that this test will correctly detect the absence of the disease is 95%.

2. 2 The disease is fairly rare, found in only 0.5% of the population. If you have a positive test (meaning that the test says “yes, you got it”) what is the probability that you really have the disease?

3. 3 Test positive Test negative TOTAL Have disease? YES Have disease? NO TOTAL100,000

4. 4 Test positive Test negative TOTAL Have disease? YES 500 Have disease? NO 99,500 TOTAL100,000

5. 5 Test positive Test negative TOTAL Have disease? YES 490 500 Have disease? NO 99,500 TOTAL100,000

6. 6 Test positive Test negative TOTAL Have disease? YES 490 10 500 Have disease? NO 99,500 TOTAL100,000

7. 7 Test positive Test negative TOTAL Have disease? YES 490 10 500 Have disease? NO 94,525 99,500 TOTAL100,000

8. 8 Test positive Test negative TOTAL Have disease? YES 490 10 500 Have disease? NO 4,975 94,525 99,500 TOTAL100,000

9. 9 Test positive Test negative TOTAL Have disease? YES 490 10 500 Have disease? NO 4,975 94,525 99,500 TOTAL 5,465 100,000

10. 10 Test positive Test negative TOTAL Have disease? YES 490 10 500 Have disease? NO 4,975 94,525 99,500 TOTAL 5,465 94,535 100,000

11. 11 Test positive Test negative TOTAL Have disease? YES 490 10 500 Have disease? NO 4,975 94,525 99,500 TOTAL 5,465 94,535 100,000 Among those with a positive test, the proportion with The disease is (about 9%).

12. 12 Test positive Test negative TOTAL Have disease? YES 490 10 500 Have disease? NO 4,975 94,525 99,500 TOTAL 5,465 94,535 100,000 Among those with a negative test, the proportion with out the disease is (99.9894%).