Table 1.
ROC Analysis: Sensitivity and Specificity of Expired CO Output (N = 662)
| CO cutoff | Sens | Spec | PPV | NPV | Eff | False − (n)a | False + (n)a |
|---|---|---|---|---|---|---|---|
| 0 | 1 | 0 | .94 | .99 | .944 | 0 | 37 |
| 1 | .998 | .108 | .95 | .8 | .949 | 1 | 33 |
| 2 | .99 | .541 | .97 | .77 | .965 | 6 | 17 |
| 3 | .981 | .811 | .99 | .71 | .971 | 12 | 7 |
| 4 | .957 | .838 | .99 | .53 | .950 | 27 | 6 |
| 5 | .938 | .838 | .99 | .44 | .932 | 39 | 6 |
| 6 | .907 | .838 | .99 | .35 | .903 | 58 | 6 |
| 7 | .877 | .865 | .99 | .29 | .876 | 77 | 5 |
| 8 | .85 | .919 | .99 | .27 | .854 | 94 | 3 |
| 9 | .829 | .946 | 1 | .25 | .836 | 107 | 2 |
| 10 | .794 | .946 | 1 | .21 | .802 | 129 | 2 |
| 11 | .749 | .973 | 1 | .19 | .762 | 157 | 1 |
| 12 | .698 | .973 | 1 | .16 | .713 | 189 | 1 |
| 13 | .655 | .973 | 1 | .14 | .673 | 216 | 1 |
| 14 | .594 | .973 | 1 | .12 | .615 | 254 | 1 |
| 15 | .550 | .973 | 1 | .11 | .573 | 281 | 1 |
Note. Bold and italic values correspond to ideal cut-off value. ROC = receiver operating characteristics; CO cutoff = carbon monoxide (CO) level in ppm used as cutoff to identify smokers (i.e., positive cotinine outcome); sens = sensitivity (i.e., proportion of smokers accurately identified; positive outcome); spec = specificity (i.e., proportion of nonsmokers accurately identified; negative outcome); PPV = positive predictive value (i.e., the percent of participants identified as smokers who are actually smokers); NPV = negative predictive value (i.e., the percent of participants identified as nonsmokers who are actually nonsmokers); eff = efficiency (i.e., weighted average of sensitivity and specificity taking into account disease prevalence); false − = false negatives (i.e., smokers mislabeled as “nonsmokers”); false + = false positives (i.e., nonsmokers mislabeled as “smokers”).
aActual smoking status: 37 nonsmokers (i.e., negative cotinine) and 625 smokers (i.e., positive cotinine).