Table 3.

Performance of biochemical indicators and combinations with self-report as the reference measure.

Biochemical indicator	Biochemical indicator cut-off	True positives	True negatives	False positives	False negatives	Sensitivity	Specificity	Efficiency	Positive likelihood ratio	Negative likelihood ratio	Positive predictive value (%)	Negative predictive value (%)
						(%)	(%)	(%)
Breath CO	≥5	85	80	2	5	94.4	97.6	95.9	38.72	0.06	97.7	94.1
Urine NicAlert	≥3	83	80	2	7	92.2	97.6	94.8	37.80	0.08	97.7	92.0
Saliva NicAlert	≥1	69	70	12	21	76.7	85.4	80.8	5.23	0.27	85.2	76.9
Breath CO/urine NicAlert	≥5/≥3	88	78	4	2	97.8	95.1	96.5	20.04	0.02	95.7	97.5
Breath CO/saliva NicAlert	≥5/≥1	88	68	14	2	97.8	82.9	90.7	5.73	0.03	86.3	91.1
Urine NicAlert/saliva NicAlert	≥3/≥1	89	69	13	1	98.9	84.2	91.9	6.24	0.01	87.3	98.6

True positive: self-reported smoker and indicator smoker. True negative: self-reported non-smoker and indicator non-smoker. False positive: self-reported non-smoker and indicator smoker. False negative: self-reported smoker and indicator non-smoker. CO: carbon monoxide. NicAlert is a Registered Trademark.