Population characteristics
| Lung function (FEV1 and FVC) and NO2 population# | Lung function (FEV1 and FVC) and PM population¶ | Excluded from analyses due to incomplete data (for lung function and NO2 population) | Difference p-value | |
| Subjects | 299 537 | 278 228 | 203 082 | |
| Sex | ||||
| Male | 47.1 (140 977) | 47.2 (131 257) | 43.4 (88 187) | <0.001 |
| Female | 52.9 (158 560) | 52.8 (146 971) | 56.6 (114 895) | |
| Age years | 56±8.05 | 56±8.05 | 57.3±8.1 | <0.001 |
| Age | ||||
| <65 years | 83.2 (249 067) | 83.1 (231 221) | 77.6 (157 526) | <0.001 |
| ≥65 years | 16.8 (50 470) | 16.9 (47 007) | 22.4 (45 556) | |
| BMI kg·m−2 | 27.4±4.68 | 27.4±4.69 | 27.6±4.97 | <0.001 |
| Missing data | 3105 | |||
| BMI | ||||
| Normal (<25 kg·m−2) | 33.3 (99 832) | 33.3 (92 673) | 32.7 (65 350) | <0.001 |
| Overweight (25–29.9 kg·m−2) | 43.2 (129 271) | 43.1 (120 024) | 41.4 (82 872) | |
| Obese (≥30 kg·m−2) | 23.5 (70 434) | 23.6 (65 531) | 25.9 (51 755) | |
| Missing data | 3105 | |||
| Education level | ||||
| A-level, O-level or CSEs | 51.3 (153 657) | 51.9 (144 504) | 61.7 (119 076) | <0.001 |
| College, university, NVQ or other professional qualifications | 48.7 (145 880) | 48.1 (133 724) | 38.3 (73 864) | |
| Missing data | 10 142 | |||
| Household income | ||||
| <GPB 31 000 | 44.2 (132 527) | 44.6 (124 097) | 57.9 (72 891) | <0.001 |
| ≥GBP 31 000 | 55.8 (167 010) | 55.4 (154 131) | 42.1 (52 993) | |
| Missing data | 77 198 | |||
| Smoking status | ||||
| Never-smoker | 59.0 (176 817) | 58.8 (163 686) | 48.4 (96 773) | <0.001 |
| Former smoker | 38.1 (114 249) | 38.3 (106 658) | 29.4 (58 842) | |
| Current smoker | 2.8 (8 471) | 2.8 (7 884) | 22.2 (44 515) | |
| Missing data | 2952 | |||
| Passive smoking exposure at home | ||||
| None | 94.7 (283 521) | 94.8 (263 679) | 93.6 (142 028) | <0.001 |
| Any | 5.3 (16 016) | 5.2 (14 549) | 6.4 (9 781) | |
| Missing data | 51 273 | |||
| Asthma | ||||
| Never had asthma | 89.4 (267 490) | 89.3 (248 232) | 89.3 (179 670) | 0.53 |
| Ever had asthma | 10.6 (31 818) | 10.7 (29 779) | 10.7 (21 498) | |
| Missing data | 229 | 217 | 1914 | |
| Occupational status | ||||
| Non-“at-risk” occupation | 98.2 (206 506) | 98.2 (192 826) | 96.4 (112 765) | <0.001 |
| “At-risk” occupation | 1.8 (3724) | 1.8 (3552) | 3.6 (4165) | |
| Missing data | 89 307 | 81 850 | 86 152 | |
| FEV1 L | 2.9±0.78 | 2.9±0.78 | 2.6±0.77 | <0.001 |
| Missing data | 116 641 | |||
| FVC L | 3.8±1.00 | 3.8±1.00 | 3.5±0.98 | <0.001 |
| Missing data | 116 641 | |||
| FEV1/FVC | 0.8±0.07 | 0.8±0.07 | 0.8±0.08 | <0.001 |
| Missing data | 116 641 | |||
| COPD | ||||
| No | 92.7 (276 948) | 92.6 (257 089) | 87.9 (74 762) | <0.001 |
| Yes | 7.3 (21 900) | 7.4 (20 478) | 12.1 (10 267) | |
| Missing data | 689 | 661 | 118 053 |
Data are presented as n, % (n) or mean±sd, unless otherwise stated. FEV1: forced expiratory volume in 1 s; FVC: forced vital capacity; NO2: nitrogen dioxide; PM: particulate matter; BMI: body mass index; CSE: Certificate of Secondary Education; NVQ: National Vocational Qualification; COPD: chronic obstructive pulmonary disease. #: descriptive statistics shown are for participants with complete data for FEV1 and FVC, age, sex, BMI, education level, household income, smoking status, passive smoking exposure at home and residential NO2 exposure; ¶: descriptive statistics shown are for participants with complete data for FEV1 and FVC, age, sex, BMI, education level, household income, smoking status, passive smoking exposure at home and residential PM exposure.