Baseline summary descriptive data (measured when the children were 18 months old), n (% or mean±SD)
| Variables | No of observations | ||
| All households | Non-smoker households | Smoker households | |
| Total | 18 845 (100.0) | 7130 (100.0) | 11 651 (100.0) |
| Parent’s characteristics | |||
| Father’s age (years) | 18 845 (36.5±13.8) | 7130 (35.7±9.1) | 11 651 (36.9±15.6) |
| <25 | 475 (2.5) | 53 (0.7) | 419 (3.6) |
| 25–29 | 3440 (18.3) | 858 (12.0) | 2574 (22.1) |
| 30–34 | 6592 (35.0) | 2729 (38.3) | 3859 (33.1) |
| ≥35 | 8338 (44.2) | 3490 (49.0) | 4799 (41.2) |
| Mother’s age (years) | 18 845 (29.9±4.8) | 7130 (31.4±4.3) | 11 651 (28.9±4.9) |
| <25 | 2707 (14.4) | 409 (5.7) | 2283 (19.6) |
| 25–29 | 6117 (32.4) | 1848 (25.9) | 4251 (36.5) |
| 30–34 | 6760 (35.9) | 3236 (45.4) | 3510 (30.1) |
| ≥35 | 3261 (17.3) | 1637 (23.0) | 1607 (13.8) |
| Father’s education level | |||
| Junior high or below | 2500 (13.3) | 409 (5.7) | 2079 (17.8) |
| Senior high | 7454 (39.6) | 1772 (24.9) | 5664 (48.6) |
| Junior college | 4134 (21.9) | 1790 (25.1) | 2332 (20.0) |
| College and above | 4623 (24.5) | 3140 (44.0) | 1479 (12.7) |
| Missing | 134 (0.7) | 19 (0.3) | 97 (0.8) |
| Mother’s education level | |||
| Junior high or below | 2637 (14.0) | 521 (7.3) | 2103 (18.1) |
| Senior high | 7526 (39.9) | 1927 (27.0) | 5571 (47.8) |
| Junior college | 4797 (25.5) | 2147 (30.1) | 2638 (22.6) |
| College and above | 3852 (20.4) | 2527 (35.5) | 1314 (11.3) |
| Missing | 33 (0.2) | 8 (0.1) | 25 (0.2) |
| Parents’ employment status | |||
| Father employed | 18 053 (95.8) | 6969 (97.7) | 11 075 (95.1) |
| Missing | 182 (1.0) | 9 (0.1) | 121 (0.6) |
| Mother employed | 11 475 (60.9) | 4698 (65.9) | 6733 (57.8) |
| Missing | 108 (0.6) | 9 (0.1) | 92 (0.5) |
| Parents’ smoking status | |||
| Only father smokes | 8854 (47.0) | 0 (0.0) | 8854 (76.0) |
| Only mother smokes | 87 (0.4) | 0 (0.0) | 87 (0.7) |
| Both parents smoke | 923 (4.9) | 0 (0.0) | 923 (7.9) |
| None of them smoke | 8760 (46.5) | 7130 (100.0) | 1630 (14.0) |
| Missing | 221 (1.2) | 0 (0.0) | 157 (1.4) |
| Parents’ smoking intensity (smokers) | |||
| Father’s cigarettes per day | 9782 (15.2±9.5) | 0 (–) | 9782 (15.2±9.4) |
| Mother’s cigarettes per day | 1052 (9.3±6.8) | 0 (–) | 1052 (9.3±6.8) |
| Children’s characteristics | |||
| Child being a boy | 9912 (52.6) | 3765 (52.8) | 6114 (52.5) |
| First-born child | |||
| Yes | 9468 (50.2) | 3579 (50.2) | 5845 (50.2) |
| No | 9367 (49.7) | 3551 (49.8) | 5796 (49.7) |
| Missing | 10 (0.1) | 0 (0.0) | 10 (0.1) |
| Children’s SHS exposure | |||
| General SHS exposure | |||
| Never | 8441 (44.8) | 4439 (62.3) | 3961 (34.0) |
| Ever | 10 401 (55.2) | 2691 (37.7) | 7690 (66.0) |
| Missing | 3 (0.0) | 0 (0.0) | 0 (0.0) |
| SHS intensity* | |||
| Non-heavy SHS exposure | 16 659 (88.4) | 6968 (97.7) | 9632 (82.7) |
| Heavy SHS exposure | 2183 (11.6) | 162 (2.3) | 2019 (17.3) |
| Missing | 3 (0.0) | 0 (0.0) | 0 (0.0) |
| Household characteristics | |||
| Family income (NTD) | |||
| <30 000 | 2195 (11.6) | 449 (6.3) | 1705 (14.6) |
| 30 000–1 00 000 | 14 332 (76.1) | 5319 (74.6) | 8996 (77.2) |
| >1 00 000 | 2249 (11.9) | 1348 (18.9) | 900 (7.7) |
| Missing | 69 (0.4) | 14 (0.2) | 50 (0.4) |
| No of smokers in the family | 18 821 (0.9±1.0) | 7130 (0.0±0.0) | 11 628 (1.4±0.9) |
40 New Taiwan Dollars (NTD)≒£1; 30 NTD≒1 US$.
*Heavy SHS: mother reported ‘often’ or ‘every day’ to the question “How often is your baby exposed to secondhand smoke?”; non-heavy SHS: ‘never’ or ‘occasionally’ to that question.
SHS, secondhand smoke.