Question

Consider two medical tests, A and B for a virus. Test A is 95% effective at recognizing the virus when it is present but has a 10% false positive rate (indicating that the virus is present, when it is not). Test B is 90% effective at recognizing the virus, but has a 5% false positive rate. The two tests use independent methods of identifying the virus. The virus is carried by 1% of all people. Say that a person is tested for the virus using only one of the tests and that test comes back positive for carrying the virus. Which test returning positive is more indicative of someone really carrying the virus?

Answer 1

Answer:

Test B.

Explanation:

Test A - 95% effective with 10% false positive rate.

Test B -90% effective with 5% false positive rate.

Test A and B are independent methods.

One of the tests is carried out on a person and turns out to be positive.

To calculate the effectiveness of the test,

  Test A = Effectiveness in  percentage divided  by the false positive rate.

                   95/10 = 9.5

 

  Test B  = Effectiveness in  percentage divided  by the false positive rate.

                   90/5 = 18.

   

Test B has a higher effective rate than Test A.

Therefore Test B is more indicative of a positive result than Test A.