Question

An early COVID-19 serology showed an approximate sensitivity and specificity consistent with the table below. Although unknown, a 5% prevalence of COVID-19 was assumed.

	SARS-CoV-2 Present	SARS-CoV-2 Absent
Test positive	47	18
Test negative	3	432

a. Based on the table, what is the sensitivity of the test?

b. Based on the above table, what is the estimated negative predictive value (NPV) for the test?

c. How would you interpret the above NPV number for someone unfamiliar with epidemiology and diagnostic testing?

d. What are the implications of the above NPV for the usefulness of the test for screening? Why?

Answer 1

The whole explanation will require too much time and space. So Providing the answer in the simplest possible way.

Here, a=47, b=18, c=3, d=432.

a) Sensitivity= {a÷(a+c) }×100 = {47÷(47+3) }×100 } =84.

b) NPV= {d÷(c+d) }×100 = {432÷(3+432) }×100= 99.3.

c) It is the ability of a screening test to identify those who have the disease out of those who have been tested negative.

d) The above result implies that the screening has been carried out correctly as the persons not having the disease have been tested negative. This proves that the screening has been successful.