Table 1.
Comparison between children in the study population (who had complete data on all exposures, outcomes and confounders) and those with incomplete data
| Variable | Study population N = 5780 (%) | Incomplete N differs by variable (%) |
|---|---|---|
| Sex | N = 8198 | |
| Girl | 48.8 | 48.1 |
| Child's ethnic group* | N = 6303 | |
| White | 96.8 | 93.3 |
| Child's age-outcome questionnaire* | N = 2382 | |
| ≤91 months | 67.3 | 54.7 |
| Mother's age at delivery (%)* | N = 5968 | |
| ≤20 | 1.9 | 10.9 |
| 21–25 | 15.9 | 28.9 |
| 26–30 | 43.8 | 36.1 |
| 31–35 | 29.8 | 18.4 |
| ≥36 | 8.6 | 5.8 |
| Mode of birth | N = 5968 | |
| Caesarean | 10.1 | 11.0 |
| Birthweight* | N = 8018 | |
| Normal (≥2500 g) | 96.3 | 93.4 |
| Gestation time* | N = 8198 | |
| Normal (≥37 wk) | 95.5 | 92.9 |
| Child breastfed* | N = 5547 | |
| ≥6 months | 34.7 | 22.5 |
| <6 months | 46.0 | 48.0 |
| Never | 19.3 | 29.6 |
| Marital status of mother* | N = 7307 | |
| Married | 84.4 | 67.4 |
| Home ownership status* | N = 7247 | |
| Mortgaged/Owned | 85.5 | 63.7 |
| Privately rented | 5.1 | 8.9 |
| Council rented | 7.3 | 22.9 |
| Other | 2.2 | 4.5 |
| Mother's highest qualification* | N = 6638 | |
| Degree | 17.7 | 8.7 |
| A-level | 27.2 | 18.5 |
| Below A-level | 55.1 | 72.9 |
| Difficulty in paying for food* | N = 2523 | |
| Not difficult | 97.1 | 95.1 |
| Difficult | 2.9 | 4.9 |
| Antibiotics 0–6 months* | N = 5653 | |
| No | 69.1 | 66.5 |
| Yes, only once | 22.2 | 21.7 |
| Yes, twice or more | 8.7 | 11.9 |
| Antibiotics 6–15 months | N = 5240 | |
| No | 46.8 | 45.7 |
| Yes, only once | 26.8 | 26.0 |
| Yes, twice or more | 26.5 | 28.3 |
| Antibiotics 15–24 months* | N = 4605 | |
| No | 54.0 | 50.6 |
| Yes, only once | 25.9 | 24.3 |
| Yes, twice or more | 20.2 | 25.2 |
| Asthma in past 12 months* | N = 2410 | |
| Yes | 10.9 | 13.4 |
| Doctor has ever said child has asthma | N = 2351 | |
| Yes | 19.3 | 23.2 |
| Eczema in past 12 months* | N = 2406 | |
| Yes | 17.2 | 14.3 |
| Hay fever in past 12 months | N = 2386 | |
| Yes | 8.7 | 8.9 |
| Sensitization to allergens† | N = 4173 | N = 2453 |
| Yes | 19.9 | 21.2 |
| Early wheeze 0–6 months* | N = 5677 | |
| Yes | 19.0 | 24.2 |
| Early wheeze 6–18 months* | N = 5276 | |
| Yes | 20.1 | 23.5 |
| Time child spends outdoors per week* | N = 4541 | |
| ≥7 h | 78.3 | 74.5 |
| Maternal disinfectant use during pregnancy* | N = 7347 | |
| <Once a week | 37.3 | 31.1 |
| Once a week | 37.4 | 33.9 |
| >Once a week | 25.3 | 35.0 |
| Maternal smoking in first 3 months of pregnancy* | N = 7378 | |
| No | 16.4 | 31.8 |
| Child had weekly contact with cats at 24 months | N = 4642 | |
| No contact | 45.3 | 41.9 |
*
p < 0.05 in Chi-squared test.
†
Skin sensitisation (atopy) data only available for 4173 children in the study population.