Table 1.
Contingency table and test statistics from ANSI (2010)
| Result | Failed PortaCount (FFPC < RFF∗) | Passed PortaCount (FFPC > RFF) |
|---|---|---|
| Passed MT (FFMT > RFF) | A | B |
| Failed MT (FFMT < RFF) | C | D |
| Statistics | Equation | Value | Level of endorsement |
|---|---|---|---|
| Test sensitivity | C/(A + C) | ≥0.95 | Mandatory |
| Predictive value of a pass | B/(A + B) | ≥0.95 | Advised |
| Test specificity | B/(B + D) | ≥0.50 | Advised |
| Predictive value of a fail | C/(C + D) | ≥0.50 | Advised |
| Kappa statistics | (Po† − Pe‡)/(1 − Pe‡) | >0.7 | Recommended |
∗
RFF (Reference Fit Factor) means OSHA's pass/fail criterion; half mask FF = 100, full facepiece FF = 500. FFPC means FF determined by PortaCount, and FFMT means FF determined by MT.
†
Po = (B + C)/(A + B + C + D).
‡
Pe = [(A + B) (B + D) + (C + D) (A + C)]/(A + B + C + D)2.