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Exercise 2.28
Answers
- (a)
- (b)
- Suppose our population consists of
people, and only one percent of them is afflicted with the disease. So,
people have the disease and
people don’t. Suppose the specificity and sensitivity of our test are
percent. Then, out of the
people who have the disease,
test positive and
test negative, and out of the
people who do not have the disease,
test negative and
test positive.
Thus,
Here, we can see why specificity matters more than sensitivity. Since, the disease is rare, most people do not have it. Since specificity is measured as a percentage of the population that doesn’t have the disease, small changes in specificity equate to much larger changes in the number of people than in the case of sensitivity.
