Tobacco Smoke Exposure, (N = 16,900). (a) Percent distribution of the natural log of urinary NNAL [ng/mL] by tobacco smoke exposure level, overlaid with cutpoints (purple dashed lines) selected with the Total Accuracy criterion from cumulative ROC curves. (b) Cumulative ROC curves (focused on upper-left quadrant) indicating coordinates for Total Accuracy cutpoints: none vs. second-hand smoke (SHS), smoker (green) and none, SHS vs. smoker (orange).