Figure 2.

Association of child cotinine level with maternal smoking behavior at age 15. The bar chart shows the means of child’s cotinine level (ng/ml serum) at age 15 years within nonsmokers by number of cigarettes the mother smokes per day (none, 1–5, 6–10, 11–20, more than 20) measured at the same timepoint. A kernel density plot has been superimposed over this graph to show the density of children by the number of cigarettes the mother smokes per day. This graph shows an increasing mean of cotinine level as the number of cigarettes the mother smokes per day increases although this pattern reverses in very heavy smokers (20+ cigarettes/day). The density of the population decreases as the number of cigarettes smoked per day increases.