Question

Community health workers were conducting a screening test for diabetes. People who tested positive on the screening test were referred for follow-up testing to confirm if they had diabetes. There were 300 people who tested positive during the screening in the community. Thirty of these people were later found to not have diabetes. There were 500 people who tested negative during the screening in the community. The community health workers later found out that 20 of the people who tested negative during the screening in the community did actually have diabetes.

a. How many false positives were there on the screening test?

b. How many true negatives were there on the screening test?

c. Calculate and interpret the sensitivity of the test. (show your work)

d. Calculate and interpret the specificity of the test. (show your work)

e. Calculate and interpret the positive predictive value of the test. (show your work)

f. Calculate and interpret the negative predictive value of the test. (show your work)

Answer 1

A. 30 people are found false positive.

B. 20 people are found false negative.

For more clarity am assuming:

A as True positive = 270.

B as  False positive= 30.

C as False Negative = 20.

D as True Negative = 480.

C. Sensitivity: A/(A+C) × 100.

= 270/(270+20)*100 = 93.10 %

D. Specificity: D/(D+B) × 100.

= 480/(480+30)*100 = 94.11 %.

E. Positive Predictive Value: A/(A+B) × 100.

= 270/(270+30)*100 = 90 %

F. Negative Predictive Value: D/(D+C) × 100.

= 480/(480+20) = 96%.