Question

A screening test wished to improve the diagnostic ability to identify Zika-infected fetuses in pregnancy rather than after birth. A total of 330 pregnant women (carrying one baby each) in Miami were tested. A total of 36 babies had Zika; 24 of whom tested positive. A total of 300 babies tested negative for the virus. What is the sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of the test?

a. 94.5%
b. 33.3%
c. 66.7%
d. 96.0%
e. 98.0%
f. 80.0%

Answer 1

Sensitivity = 66.7% (C)

specificity= 98.0% (E)

positive predictive value = 80.0% (F)

Negative predictive value = 96.0% (D)

accuracy of the test = 94.5% (A)

Explanation:

Given the data in the question;

Disease Present Disease Absent Total

Test Positive 24 6 30

Test Negative 12 288 300

Total 36 294 330

so A = 24, B = 6, C = 12 and D = 288

sensitivity = [A/(A+C)]×100 = [24/(24+12)]×100 = [24/36]×100

Sensitivity = 66.7% (C)

specificity= [D/(D+B)]×100 = [288/(288+6)]×100 = [288/294]×100

specificity= 98.0% (E)

positive predictive value = [A/(A+B)]×100 = [24/(24+6)]×100

= [24/30]×100

positive predictive value = 80.0% (F)

Negative predictive value = [D/(D+C)]×100 = [288/(288+12)]×100

= [288/300]×100

Negative predictive value = 96.0% (D)

accuracy of the test = [A+D/(A+B+C+D)]×100 = [24+288/(24+6+12+288)]×100

= [312/330]×100

accuracy of the test = 94.5% (A)

Nothing 33.3% (B)