Question

In May 2012, the FDA approved the first over-the-counter test for HIV, the virus that causes AIDS. In a news story on July 3, 2012, the Associated Press reported that, “When used by professionals, the test is shown to accurately identify both carriers and non-carriers [of the HIV virus] 99 percent of the time.” But a trial conducted by the company that developed the test showed that individuals using the test on themselves at home correctly detected HIV in those carrying the virus only 92 percent of the time.

What do the percentages in the paragraph tell us about the specificity and sensitivity of the test when given at home and when given by a professional?

Suppose that this test was administered by a professional (instead of at home) to a group of 10,000 people, of which 1% are infected with HIV. Fill in the following table in order to gather data on the test’s effectiveness.

Answer 1

We know,

In case of test given by a professional,

• Sensitivity = 0.99
• Specificity = 0.99

In case of test given at home,

• Sensitivity = 0.92
• no report about specificity (at home)

Test administered by a professional to a group of 10000 people with 1% infected by HIV-

Data regarding the given situation is as follows.

Based on observed frequencies we observe different measures as follows.

Regarding test's effectiveness we can conclude as follows.

• Test detects 99% of positive case successfully.
• Test detects 99% of negative case successfully.
• If test shows positive result, then there there is only 50% change to really being infected.
• If test shows negative result, then there there is as high as 99.99% change to really not being infected.