5. An investigator wants to assess the usefulness of a certain symptom (S) in th

Question

5. 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.

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 value of the S?

f) What is the predictive value negative of S?

g) What is the predictive value positive if the prevalence of disease is 0.02? 0.2?

6. TRUE OR FALSE (Extra credit if you can rewrite false statements correctly)

a) Every sample should have the same standard deviation.        ______

b) A simple random sample is a non-probability sample.              ______

c) Population parameters are calculated statistics.                       ______

d) A simple random sample is representative of the population.   ______

Explanation / Answer

The Confusion Matrix is shown below:

a.)

False Positive = 17

b.)

False Negative = 26

c.)

Sensitivity = TP / TP + FN = 774/800 = 0.9675

d.)

Specificity = TN / TN + FP = 1263 / 1280 = 0.9867

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