Question

A screening examination was performed on 250 persons for Factor X, which is found in disease Y. A definitive diagnosis for disease Y among the 250 persons had been obtained previously. The results are charted below:

TEST RESULTS Disease Present Disease Absent
Positive for Factor X 40 60
Negative for Factor X 10 140

The specificity of this test is expressed as:________

Answer 1

The specificity of this test is expressed as:________

70%.

Explanation:

a) Data and Calculations:

TEST RESULTS Disease Present Disease Absent Total

Positive for Factor X 40 60 100

Negative for Factor X 10 140 150

Total 50 200 250

Negative for X and Disease Absent = 140/200 * 100

= 0.7 * 100

= 70%

b) The specificity refers to the percentage of people who test negative for a specific disease among a group of people who do not have the disease. No test is 100% specific because some people who do not have the disease X will test positive for it (false positive). Therefore, we are testing for the true negative, that the 140 people who tested out of the 200 people who do not have the disease.