Table 1

Test measures

Reference standardOutcomeTest measures
PositiveNegative
Diagnostic algorithm
 PositiveTrue positives correctly identified (A)False positives (B)Total identified as positivePPV=A/(A+B)
 NegativeFalse negatives (C)True negatives correctly identified (D)Total identified as negativeNPV=D/(C+D)
OutcomeTrue positivesTrue negatives
Test measuresSensitivity=A/(A+C)Specificity=D/(B+D)