Question

Suppose that 1% of all people have a particular disease. A test for the disease is 99% accurate. This means that a person who has the disease has a 99% chance of testing positive for the disease, while a person who doesn't have the disease has a 99% chance of testing negative for the disease. If a person tests positive for the disease, what is the chance (rounded to the nearest hundredth) that he or she actually has the disease?

Answer 1

A positive result shows that the person is having the particular disease which he was tested for and negative result shows that the person does not have the disease for which he was tested.

If a test for the disease is 99% accurate that means that a person who has the disease has a 99% chance of testing positive for the disease, while a person who doesn't have the disease has a 99% chance of testing negative for the disease.

Therefore if a person tests positive for the disease than there is 99% chance that the person has that disease because the test is 99% accurate.