Question

3. Among 200 persons with negative screening tests for HIV antibody, 140 are negative with HIV virus (POST RATIONALE FOR ANSWER).

A. The most appropriate measure is:

a. sensitivity b. specificity c. predictive value positive d. predictive value negative

B. Estimate the value of this measure and interpret it (POST RATIONALE FOR ANSWER):

Answer 1

Solution:

A. The most appropriate measure is specificity.

Specificity: The ability of a test to correctly indentify an individual as disease free is known as test specificity. ​​​​

Here, in our question data is given about the number of individuals who have negative HIV virus i.e. number of individuals who are free from disease. Therefore specificity is appropriate measure for the given question.

B. Number of individuals with HIV negative = 140 Total number of individuals = 200

Specificity is 70%.

Interpretation: A test with 70% specificity is interpreted as follows:

If an individual truely is the case of HIV negative (disease free) then there is a 70% probability that screening test will identify the individual as HIV negative (disease free).