Characteristics of attenders and non-attenders
| Children who had any spirometry | Children who had no spirometry and were alive at 1 year | |
| Number | 7414 | 6547 |
| Mean (SD) birth weight (g) | 3412 (554) | 3369 (565) |
| Mean (SD) gestation (weeks) | 39.4 (1.9) | 39.4 (1.9) |
| Male, N (%) | 3692 (49.8) | 3520 (53.8) |
| Maternal smoking, N (%) | 1372/7248 (18.9) | 2033/5896 (34.5) |
| Manual workers, N (%) | 2606/6817 (38.2) | 2407/4681 (51.4) |
| Exclusively breast fed for at least 3 months, N (%) | 862/7259 (11.9) | 470/5408 (8.7) |