Test accuracy of the final risk score in the external validation sample
| Discrimination characteristics | Application of the score assuming 5.5% prevalence of undiagnosed COPD | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Score threshold | Sensitivity (%) | Specificity (%) | Correctly classified (%) | LR+ | LR− | PPV (%) | NPV (%) | Screening yield (%) | NNS | Clinical assessments per case detected |
| 0 | 100 | 0 | 35.0 | 1 | – | 5.5 | – | 5.50 | 19 | 19 |
| 0.5 | 96.1 | 34.7 | 56.2 | 1.47 | 0.11 | 7.9 | 99.3 | 5.29 | 19 | 13 |
| 1 | 90.6 | 51.9 | 65.5 | 1.88 | 0.18 | 9.9 | 99.0 | 4.98 | 21 | 11 |
| 1.5 | 89.4 | 55.1 | 67.1 | 1.99 | 0.19 | 10.4 | 98.9 | 4.92 | 21 | 10 |
| 2 | 81.2 | 71.9 | 75.2 | 2.89 | 0.26 | 14.4 | 98.5 | 4.47 | 23 | 7 |
| 2.5 | 63.2 | 87.4 | 79.0 | 5.02 | 0.42 | 22.6 | 97.6 | 3.48 | 29 | 5 |
| 3 | 55.8 | 91.9 | 79.3 | 6.89 | 0.48 | 28.6 | 97.3 | 3.07 | 33 | 4 |
| 3.5 | 47.6 | 94.6 | 78.1 | 8.80 | 0.55 | 33.9 | 96.9 | 2.62 | 39 | 3 |
| 4 | 40.4 | 95.8 | 76.4 | 9.57 | 0.62 | 35.8 | 96.5 | 2.22 | 45 | 3 |
| 4.5 | 23.2 | 98.3 | 72.0 | 13.5 | 0.78 | 44.0 | 95.6 | 1.28 | 79 | 3 |
| 5 | 20.6 | 98.4 | 71.2 | 13.1 | 0.81 | 44.3 | 95.5 | 1.13 | 89 | 3 |
| 5.5 | 11.3 | 99.5 | 68.6 | 21.5 | 0.89 | 55.8 | 95.1 | 0.62 | 161 | 2 |
| 6 | 5.53 | 99.7 | 66.7 | 18.9 | 0.95 | 50.9 | 94.8 | 0.30 | 329 | 2 |
| 6.5 | 3.23 | 99.8 | 65.0 | 19.4 | 0.97 | 52.5 | 94.7 | 0.18 | 563 | 2 |
Correctly classified= proportion of participants with disease status correctly classified.
LR, likelihood ratio (ie, the ratio by which the pretest probability is altered by a positive or negative test result);
NPV, negative predictive value (proportion of all participants with a negative test who are disease free);
NNS, number-needed-to-screen (the number of patients or patient records the risk score would need to be applied to) to identify one patient with COPD; NPV, negative predictive value (proportion of all subjects with a negative test who are disease free); PPV, positive predictive value (proportion of all participants with a positive test who have disease); Screening yield, proportion of all patients subjected to the risk score who would be correctly identified as having COPD.
COPD, chronic obstructive pulmonary disease.