An investigator wants to assess the usefulness of a certain symptom (S) in the diagnosis of a particular disease (D). In a random sample of 800 patients with the disease, 774 reported having the symptom. In an independent random sample of 1280 subjects without the disease, 17 reported having the symptom. (Hint: The symptom is the test)

a. Explain what a false positive would be in this situation

b. Explain what a false negative would be in this situation

c. What is the sensitivity of using the symptom (S) as a test for disease (D)?

d. What is the specificity of using S as a test for D?

e. If the prevalence of D in the population is 0.002, what is the positive predictive index of the S? (Probability of having the disease D given that the patient had symptoms S)?

f. What is the positive predictive value if the prevalence is 0.2?