Fig 1.

(A – C): Histogram of self-reported CPD and the biomarkers expired CO and plasma COT for study participants (n = 700). Cutoff values of expired CO at ≤ 10 ppm and plasma COT levels of ≤ 14 ng/ml have been traditionally used to differentiate smokers from non-smokers. Correlations are weak but significant between expired CO with CPD (D), plasma COT with CPD (E), and plasma COT with CO (F). Correlations are also significant between CO/cigarette with CPD (G) and COT/cigarette with CPD (H). Each point represents an individual. r = Pearson's correlation coefficient. Analyses were performed on log-transformed variables (CPD, expired CO, plasma COT) although raw data is plotted.