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)

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

a. Not having symptoms even though the patient has the disease

b. Having symptoms even though the patient does not have the disease

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

a. Not having symptoms even though the patient has the disease

b. Having symptoms even though the patient does not have the disease

3. What is the sensitivity of using the symptom (S) as a test for disease (D)? Which choice is correct? Please provide an explanation.

a. 0.500

b. 0.750

c. 0.968

d. 0.100

4. What is the specificity of using S as a test for D? Which choice is correct? Please provide an explanation

a. 0.500

b. 0.987

c. 0.879

d. 0.789

5. 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)? Which choice is correct? Please provide an explanation.

a. 0.128

b. 0.821

c. 0.281

d. 0.500

6. What is the positive predictive value if the prevalence is 0.2? Which choice is correct? Please provide an explanation.

a. 0.123

b. 0.321

c. 0.499

d. 0.949