Question

a new screening test for Lyme disease is being evaluated. it was administered to 1,235 people in maine. While 115 people with the disease tested positive for it another 47 people who do not have the disease tested positive for Lyme. 721 people who do not have Lyme tested negative.

1. calculate specificity

2. calculate positive predictive value

3. calculate the negative predictive value

4. would you recommend this nrw screening test?

Answer 1

(1)

From the given data, the following Table is calculated:

	Have disease	Do not have disease	Total
Test positive	a = (TP) = 115	b = (FP) = 47	a + b (TP + FP) = 162
Test negative	c = (FN) = 352	d = (TN) = 721	c + d (TN + FN) = 1073
Total	a + c (TP + FN) = 467	b + d (FP + FN) = 768	a + b + c + d = (TP + TN + FP + FN ) = 1235

Specificity is given by:

%

(2)

Positive Predictive Value (PPV) is given by:

%

(3)

Negative Predictive Value (NPV) is given by:

%

(4)

PPV = 70.99% indicates that among those who had a positive screening test, the probability of disease is 70.99%

NPV = 67.19% indicates that among those who had a negative screening test, the probability of disease free is 67.19%

Since These values are near to 100%, we would recommend this new screening test.