Figure 1.

Cotinine concentrations by self-reported smoking status. A comparison of urine cotinine concentrations with self-reported smoking status reveals potential misclassification; cotinine detection limit: 8 ng/ml; active smoking levels: >100 ng/ml (urine). Boxplots show cotinine concentrations (ng/ml, y-axis) with self-reported smoking status (420 never smokers, 458 former smokers, 63 current smokers). The bold horizontal line represents the median, the top and bottom borders of the box represent the 75^th and 25^th percentiles, respectively, while the circles represent outliers.