Child’s sex | Female*, male |
Mother’s education level | Below O level, O level only*, A level or higher, unknown |
Mother’s housing tenure | Owned/mortgaged*, council rented, non-council rented, unknown/other |
Mother’s ethnic origin | White*, non-white, unknown |
Mother’s parity | 0*, 1, 2+, unknown |
Mother’s age (years) | <20, 20–24, 25–29*, 30–34, 35+ |
Birth season | January–March, April–June, July–September, October–December* |
Breast feeding in first 6 months | No, yes*, unknown |
Day care use in first 8 months | No*, yes, unknown |
Antibiotic use in first 6 months | Never*, once, more than once, unknown |
Mother’s anxiety score in pregnancy (CCEI units)† | 0–4*, 5–9, 10+, unknown |
Pets kept in first year | No pets*, cat and/or dog, other pets only, unknown |
Maternal smoking in pregnancy (cigarettes/day)‡ | Not exposed*, passive only, 1–9/day, 10–19/day, 20+/day, unknown |
Weekend tobacco exposure in first 6 months | Not exposed*, exposed, unknown |
Mother’s body mass index (BMI) (kg/m2) | <20, 20–24.99*, 25–29.99, 30+, unknown |
Crowding in home (persons/room) | Up to 1*, 1+, unknown |
Damp and/or mould in home | No*, yes, unknown |
Child’s birthweight (g) | <2500, 2500–2999, 3000–3499*, 3500–3999, 4000+, unknown |
Child’s gestational age at birth (weeks) | <37, 37–40*, 41+ |
Multiple pregnancy | No*, yes |
Child’s head circumference (cm) | <33, 33–34.99*, 35–36.99, 37+, unknown |
Child’s birth length (cm) | <48, 48–50.99*, 51–53.99, 54+, unknown |
Mother ever had asthma | No*, yes |
Mother ever had eczema | No*, yes |
Mother ever had rhinitis | No*, yes |
Mother ever had migraine | No*, yes |
Mother’s atopic/migraine history unknown | No*, yes |
Mother had cold/flu in late gestation | No*, yes |
Mother had urinary infection in late gestation | No*, yes |
Mother had other infections in late gestation | No*, yes |
Mother’s history of infections unknown | No*, yes |