Table 5 Variations in the definitions of smoking exposures

Total/Lifetime

 ≤ 8 vs. 8 < y ≤ 18 vs. > 18y

Age at first use

Mean age

Prior to first full-term pregnancy

Within 5 years of menarche

Never vs. ≤ 18 vs. > 18yo

 ≥ 20 vs. 18–19 vs. ≤ 17yo

Pack-years

0 vs. ≤ 14 and > 0 vs. > 14py

0–5 vs. 6–20 vs. ≥ 21py

Nonsmoker vs. < 20 vs. ≥ 20py

 ≤ 2.3 vs. 2.3 < py ≤ 9.8 vs. > 9.8py

0 < py ≤ 5 vs. 5 > py ≤ 10 vs. 10py

0 vs. > 0 ≤ 4 vs. > 4py

0 vs. 1–4 vs. ≥ 5py

Packs/week

 < 2 vs. ≤ 2 packs < 5 vs. 5 ≤ packs

0 vs. > 0 < 5 vs. ≥ 5 packs/week