A two-by-two contingency table for enteric infection and diarrhoea
| Diarrhoea | |||
| Yes | No | ||
| Enteric infection | Yes | Symptomatic infection (A) | Asymptomatic infection (B) |
| No | Non-infectious diarrhoea (C) | Healthy (D) | |
Sensitivity is A/(A+B) and specificity is D/(C+D).