Table 2– Pooled estimates of effects of risk factors on stage I or higher chronic obstructive pulmonary disease (COPD),# and on percentage forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC) ratio, adjusted for all risk factors in the regression model, including pack-years of smoking
Stage I or higher COPD% FEV1/FVC
OR (95% CI)p-valueI2 %p-value for heterogeneityRegression coefficient (95% CI)p-valueI2 %p-value for heterogeneity
Females1.10 (0.85–1.43)0.46570.0041.16 (0.70–1.57)<0.001390.069
Age per 10-yr difference1.52 (1.35–1.71)<0.001600.002-2.69 (-2.88– -2.49)<0.001260.17
BMI kg·m−2
 25–300.58 (0.46– 0.72)<0.001430.0451.87 (1.29–2.45)<0.001540.008
 >300.50 (0.37–0.67)<0.001500.0202.54 (1.87–3.20)<0.001500.017
Education+0.76 (0.67–0.87)<0.001260.180.54 (0.29–0.80)<0.00100.99
Hospitalisation for breathing problems before age 10 yrs2.35 (1.42– 3.91)0.001540.011-1.35 (-2.44–-0.27)0.014320.12
Current smoking1.31 (1.00–1.72)0.049520.012-0.38 (-1.10–0.34)0.30550.007
Passive smoking§1.24 (1.05–1.47)0.01200.45-0.61 (-1.06– -0.15)0.009140.30
Doctor ever-diagnosed tuberculosis1.78 (1.17–2.72)0.007410.070-1.98 (-4.23–0.26)0.08380<0.001
Family history of COPDƒ1.50 (1.19– 1.90)0.001310.13-0.95 (-1.51– -0.39)0.001260.18
Years working in dusty jobs per 10-yr difference1.04 (0.98– 1.11)0.1700.71-0.33 (-0.50– -0.15)<0.00100.49
Regular exposure to dust in present job0.86 (0.61– 1.21)0.40360.0910.61 (-0.02–1.24)0.058280.16
Regular exposure to fumes in present job0.91 (0.67–1.24)0.5500.970.37 (-0.22–0.97)0.2270.38
Years exposed to biomass fires per 10-yr difference##
 For heating1.01 (0.94–1.10)0.7200.630.04 (-0.17–0.26)0.7100.47
 For cooking¶¶1.02 (0.68–1.54)0.9120.42-0.20 (-2.16–1.76)0.84320.15
  • BMI: body mass index. See online supplementary material for more details of model fitting and coding of risk factors. The model adjusts for a quadratic effect of pack-years of smoking, which is not shown in the table because the separate coefficients of pack-years and pack-years squared are difficult to interpret. Table 1 shows how pack-years of smoking affected prevalence of COPD at different sites. #: stage I or higher COPD defined as having an FEV1/FVC ratio below the lower limit of normal given age and sex, using reference equations from National Health and Nutrition Examination Survey. : a negative regression coefficient indicates a reduction in FEV1/FVC, i.e. poorer lung function. +: effect per group, assuming a linear effect over the four groups of highest level of education, as follows: none; primary (primary or middle school); secondary (secondary school); tertiary (technical/vocational college or university). §: somebody else smoking in the subject's home in the last 2 weeks. ƒ: doctor ever-diagnosed mother, father, sister or brother with emphysema, chronic bronchitis or COPD. ##: fires burning coal, coke, peat, wood, crop residue or dung. ¶¶: years of equivalent continuous exposure are calculated by multiplying number of years over which subject was exposed by number of hours of exposure per day divided by 24.