The association between smoking and lung function, with the regression coefficients (β) and p values for each pack-year's impact on FEV1 (ml)* and FEV1% predicted†
| n‡ | FEV1 (ml) | FEV1 (%) | |||||
| β (95% CI) | p Value | p (interaction) | β (95% CI) | p Value | p (interaction) | ||
| Subjects with COPD | |||||||
| All§ | 948 | −3.6 (−5.6 to −1.7) | 0.000 | −0.11 (−0.17 to −0.04) | 0.001 | ||
| Male¶ | 583 | −5.1 (−7.4 to −2.7) | 0.000 | −0.15 (−0.22 to −0.08) | 0.000 | ||
| Female¶ | 365 | −0.1 (−3.7 to 3.5) | 0.952 | 0.025 | 0.002 (−0.11 to 0.12) | 0.967 | 0.027 |
| Subjects without COPD | |||||||
| All§ | 954 | −3.1 (−4.6 to −1.6) | 0.000 | −0.09 (−0.13 to −0.05) | 0.000 | ||
| Male¶ | 478 | −3.2 (−5.1 to −1.2) | 0.001 | −0.06 (−0.12 to −0.01) | 0.027 | ||
| Female¶ | 476 | −3.0 (−5.4 to −0.7) | 0.011 | 0.940 | −0.13 (−0.20 to −0.06) | 0.000 | 0.124 |
p (interaction) is the p value for the interaction term gender×pack-years.
↵* Adjusted for sex, age, height, pack-years, self-reported asthma and educational level.
↵† Adjusted for sex, pack-years, self-reported asthma and educational level.
↵‡ Educational level was missing for five female subjects with COPD and one of the male subjects without COPD; asthma history was missing for one of the female subjects with COPD.
↵§ Models without an interaction term.
↵¶ Models including a gender×pack-years interaction term; gender-specific estimates obtained by the lincom command in Stata.
COPD, chronic obstructive pulmonary disease; FEV1, forced expiratory volume in 1 s.