Question

Although the concepts of sensitivity and specificity are usually applied to diagnostic laboratory or screening tests, they are equally valid for other tests that indicate the presence or absence of disease. These may be tests designed to elicit certain physical signs of disease by examination (e.g. hypertension, cervical cancer, neurological defects, and tendency to hemorrhage) or questions aimed at uncovering symptoms.

Suppose that a short psychometric questionnaire that was devised to detect undiagnosed cases of personality disorder was found, after being tested in different mental health clinics using the questionnaire on people with previously diagnosed personality disorder, to have a sensitivity of 25% and a specificity of 99%.

If 260 persons are tested using this short psychometric questionnaire, from a population with a prevalence of personality disorders of 25%, draw, fill in, and label a 2x2 table displaying this information. You can round your numbers to “whole people”

Answer 1

True Disease
No disease	Disease
P(ND)=0.75	P(D)=0.25
75.00%	25.00%
Test positive	Test negative	Test positive	Test negative
1.00%	99.00%	25.00%	75.00%
False Positive	True Negative	True positive	False negative
0.0075	0.7425	0.0625	0.1875

No disease P(ND)=0.75 75.00% Test positive Test negative 1.00% 99.00% False Positive True Negative 0.0075 0.7425 Disease P(D)=0.25 25.00% Test positive Test negative 25.00% 75.00% True positive False negative 0.0625 0.1875

for n = 260

2 X 2 table displaying the informaiton :

Population	260	Total
Test	positive	Negative
Dis	No dis
Postive	16	2	18
Negative	49	193	242
Total	65	195	260

Population 260 positive Dis 16 Test Postive Negative Total Negative No dis 2 193 195 Total 18 242 260 49 65