Table 3.

Diagnostic test table

Diagnostic test result	Disease		Total
	Present	Absent
Positive	a - True positive	b - False positive	(a + b)
Negative	c - False negative	d - True negative	(c + d)
Total	(a + c)	(b + d)
$\mathrm{Sensitivity}=\frac{a}{(a+c)}=\frac{\mathrm{TP}}{(\mathrm{TP}+\mathrm{FN})}$		$\mathrm{Specificity}=\frac{d}{(b+d)}=\frac{\mathrm{TN}}{(\mathrm{TN}+\mathrm{FP})}$
$\mathrm{PPV}=\frac{a}{(a+b)}=\frac{\mathrm{TP}}{(\mathrm{TP}+\mathrm{FP})}$		$\mathrm{NPV}=\frac{d}{(c+d)}=\frac{\mathrm{TN}}{(\mathrm{FN}+\mathrm{FN})}$
$\mathrm{LR\; for\; positive\; test}(\mathrm{LR}+)=\frac{\mathrm{sens}}{1-\mathrm{spec}}=\frac{a/(a+c)}{b/(b+d)}$
$\mathrm{LR\; for\; negative\; test}(\mathrm{LR}-\mathrm{})=\frac{1-\mathrm{sens}}{\mathrm{spec}}=\frac{c/(a+c)}{d/(b+d)}$