Need help with question 5.110

CHAPTER 5 Review Exercises 355 at additional antibodies to HIV, the virus that causes AIDS. Antibodies indicate the presence of the virus. The test and are facing is quite accurate but is not always correct. Here are s the risks to approximate probabilities of positive and negative ations, the EIA outcomes when the blood tested does and does d failure not actually contain antibodies to HIV:" ese ction? Test Result + , you are "in . . . . ...... either Antibodies present 0.9985 0.0015 ent rate is Antibodies absent 0.006 0.994 population) ..... ent 25 years Suppose that 1% of a large population carries of people. antibodies to HIV in their blood. (a) Draw a tree diagram for selecting a person from this population (outcomes: antibodies present or absent) and for testing his or her blood (outcomes: mployed EIA positive or negative). . . ............... 11, 139 (b) What is the probability that the EIA is positive for a randomly chosen person from this population? 35,137 (c) What is the probability that a person has the antibody, given that the EIA test is positive? 31,975 (Comment: This exercise illustrates a fact that is important when considering proposals for widespread testing for HIV, illegal drugs, or agents of biological 6,259 warfare: if the condition being tested is uncommon in . . ............ the population, many positives will be false-positives.) 5.110 Testing for HIV, continued. The previous exercise nt rate gives data on the results of EIA tests for the presence does the of antibodies to HIV. Repeat part (c) of that exercise plain for two different populations: dent. (a) Blood donors are prescreened for HIV risk factors, so perhaps only 0.1% (0.001) of this population carries HIV antibodies. sen (b) Clients of a drug rehab clinic are a high-risk rce? group, so perhaps 10% of this population carries HIV antibodies. ege the or (c) What general lesson do your calculations illustrate