Source: Gold et al. 1996. Reprinted with permission from the Massachusetts Medical Society, ©1996.

Note: Mean rates of pulmonary-function growth according to age, gender, and category of smoking. The circles represent youth who had never smoked and the triangles those who smoked ≥5 cigarettes/day. There were fewer than 15 observations for smokers before the age of 13 years. The numbers of observations of FEV₁ in boys who smoked ≥5 cigarettes/day were 41 at age 13, 120 at age 14, 213 at age 15, 311 at age 16, 361 at age 17, and 151 at age 18. In girls who smoked ≥5 cigarettes/day, the numbers of observations of FEV₁ were 39 at age 13, 109 at age 14, 197 at age 15, 254 at age 16, 290 at age 17, and 90 at age 18. FEF_25–75 = forced expiratory flow between 25% and 75% of the forced vital capacity; FEV₁ = forced expiratory volume in 1 second.