Response to the following problem:
Enzyme-linked immunosorbent assay (ELISA) is the most common type of screening test for detecting the HIV virus. A positive result from and ELISA has a high degree of sensitivity (to detect infection) and specificity (to detect non-infection). Suppose the probability that a person is infected with the HIV virus for a certain population is 0.015. If the HIV virus is actually present, the probability that the ELISA test will give a positive result is 0.995. If the HIV virus is not actually present the probability of a positive result from and ELISA is 0.01. If the ELISA has given a positive result, use Bayes' theorem to find the probability that the HIV virus is actually present.