Question

Table 1 below shows results obtained in a new screening test for diabetes. 10,000 people were screened. The cut-off level employed was 180mg of blood glucose per 100 ml. Everyone scoring above this level was classified as positive for diabetes. Everyone scoring below this level was classified as negative for diabetes. These results were compared to a “gold standard” test for diabetes that is considered to be completely valid. Compute and interpret the sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of the new screening test.

Table 1.

	"Gold-Standard" Test
Screening	Disease	No Disease	Total
Positive	125	25	150
Negative	375	9475	9850
Total	500	9500	10000

1. Calculate the following measures for this screening test:

Sensitivity =

Specificity =

PPV =

NPV =

Answer 1

Answer: Table 1 below shows results obtained in a new screening test for diabetes. 10,000 people were screened. The cut-off level employed was 180mg of blood glucose per 100 ml. Everyone scoring above this level was classified as positive for diabetes. Everyone scoring below this level was classified as negative for diabetes.

Solution:

a)

Sensitivity = (True positive / Total disease)*100

Sensitivity = (125/500)*100

Sensitivity = 25%

Specificity = (True negative/Total no disease)*100

Specificity = (9475/9500)*100

Specificity = 99.7368% = 99.74%

PPV = (True positive/Total test positive)*100

PPV = (125/150)*100

PPV = 83.33%

NPV = (True negative/Total test negative)*100

NPV = (9475/9850)*100

NPV = 96.1929% = 96.20%