Table 7. Incidence with PPV and NPV for two-stratum and four-stratum formats.
| Dataset | Cut-offs | Two-stratum |
Four-stratum |
|||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Positivity (C/N) (PPV, 1/PPV) |
Negativity (C/N) [NPV, 1/(1-NPV)] |
Positivity (C/N) (PPV, 1/PPV) |
Negativity (C/N) [NPV, 1/(1-NPV)] |
|||||||
| Current positivea | Current negativeb | High positivec | Positived | Negativee | Low negativef | |||||
| Sample set A (235C/266N) | Incidence Unadjusted 2.7% 4.0% | 97/25 41%/9% (0.109, 1 in 9) (0.155, 1 in 6) | 138/241 59%/91%, (0.982, 1 in 57) (0.974, 1 in 38) | 60/5 25%/2% (0.274, 1 in 4), (0.361, 1 in 3) | 37/20 16%/7% (0.055, 1 in 18) (0.080, 1 in 12) | 119/179 51%/68% (0.980, 1 in 49) (0.970, 1 in 33) | 19/62 8%/23% (0.990, 1 in 105) (0.986, 1 in 70) | |||
| Sample set B (336C/415N) | Incidence Unadjusted 2.7% 4.0% | 99/41 30%/10% (0.076, 1 in 13) (0.111, 1 in 9) | 237/374 70%/90% (0.979, 1 in 47) (0.968, 1 in 32) | 56/15 17%/4% (0.113, 1 in 9) (0.161, 1 in 6) | 43/26 13%/6% (0.054, 1 in 19) (0.078, 1 in 13) | 196/284 58%/68% (0.977, 1 in 43) (0.966, 1 in 29) | 41/90 12%/22% (0.985, 1 in 65) (0.977, 1 in 44) | |||
| Sample set C (36C/811N) | Incidence Unadjusted 2.7% 4.0% | 13/71 36%/9% (0.103, 1 in 10) (0.147, 1 in 7) | 23/740 64%/91% (0.981, 1 in 53) (0.972, 1 in 35) | 7/15 19%/2% (0.226, 1 in 4) (0.305, 1 in 3) | 6/56 17%/7% (0.063, 1 in 16) (0.091, 1 in 11) | 17/492 47%/60% (0.979, 1 in 47) (0.969, 1 in 32) | 6/248 17%/31% (0.985, 1 in 67) (0.978, 1 in 45) | |||
| Combined (607C/1492N) | Incidence Unadjusted 2.7% 4.0% | 209/137 34%/9% (0.094, 1 in 11) (0.135, 1 in 7) | 398/1,355 66%/91% (0.980, 1 in 51) (0.971, 1 in 34) | 123/35 20%/2% (0.193, 1 in 5) (0.265, 1 in 4) | 86/102 14%/7% (0.054, 1 in 18) (0.079, 1 in 13) | 332/955 55%/64% (0.977, 1 in 43) (0.966, 1 in 29) | 66/400 11%/27% (0.989, 1 in 90) (0.983, 1 in 60) | |||
| Sample set A (235C/266N) | Adjusted 2.7% 4.0% | 41%/7% (0.145, 1 in 7) (0.203, 1 in 5) | 59%/93% (0.983, 1 in 58) (0.974, 1 in 39) | 25%/0.04% (0.947, 1 in 1.06) (0.964, 1 in 1.04) | 16%/7% (0.061, 1 in 16) (0.089, 1 in 11) | 51%/69% (0.980, 1 in 50) (0.970, 1 in 34) | 8%/24% (0.991, 1 in 109) (0.986, 1 in 73) | |||
| P-valueg | 0.03/0.16 | 0.49/0.80 | 0.12/0.013 | 0.13/0.001 | ||||||
aIncludes all samples above current cut-off; bIncludes all samples below current cut-off; cIncludes all samples above high cut-off; dIncludes only samples between current and high cut-off; eIncludes only samples between current and low cut-off; fIncludes all samples below low cut-off; gP-value for comparison of percentages across Sample set A, B & C datasets (cancers/normals separately) using χ2 test. C, cancers; N, normals (cancer-free controls); NPV, negative predictive value; PPV, positive predictive value. PPV and NPV calculated for a population with a prevalence of 2.7% or 4.0% using unrounded specificity/sensitivity values.