Table 2 Formulæ employed to calculate outcomes of applying a one- or two-test diagnostic strategy to a population of 10,000 individuals with several prevalences of infections
One-Test Strategy | Two-Test Strategy | ||
|---|---|---|---|
TP1= | N x E x SenA | TP2 = | TP1 x SenB |
TN1 = | (N x (1 – E)) – (N x (1 – E) x (1 – SpecA)) | TN2 = | TN1 + (FP1 x SpecB) |
FP1 = | N x (1 – E) x (1 – SpecA) | FP2 = | FP1 x (1 – SpecB) |
FN1 = | N x E x (1 – SenA) | FN2 = | FN1 + (TP1 x (1 – SenB)) |
PPV1 = | TP1 / (TP1 + FP1) | PPV2 = | TP2 / (TP2 + FP2) |
NPV1 = | TN1 / (TN1 + FN1) | NPV2 = | TN2 / (TN2 + FN2) |
POR1 = | TP1 / FP1 | POR2 = | TP2 / FP2 |