Question

		Disease Prevalence 50%		Prevalence Disease 10%				Prevalence Disease 1%
		Yes	No		Yes	No	Yes		No
Test YES		TP   800 A	FP 100 B		TP   160 A	FP 180 B	TP 16   A		FP    198 B
Test NO		FN 200 C	TN 900 D		FN     40 C	TN 1,620 D	FN    4   C		TN 1,782 D
Totals		1,000	1,000		200	1,800	20		1,980
		Specificity=    TN    =                        TN+FP X 100- ________%		Specificity=				Specificity=

Answer 1

The formula for specificity is = d/ b+d%

Thus 900/900+100 ×100 = 90%

Disease prevalence of 10% disease specificity is 1620/ 1620+180×100= 90%

Prevalence disease of 1% disease

1782/1782+198×100= 90%