Table 1. Descriptive characteristics of analytic sample (N=40,949)*.
| Continuous variables | mean | SD | |
|---|---|---|---|
| Maternal age at child’s birth (years) | 30.2 | 4.4 | |
| Paternal age at birth (years) | 32.6 | 5.1 | |
| Maternal depressive/anxiety symptoms, Hopkins Symptoms Checklist-25 (SCL-25)† | 1.2 | 1.9 | |
| Paternal depressive/anxiety symptoms, Hopkins Symptoms Checklist-25 (SCL-25) ‡ | 1.1 | 2.1 | |
| Maternal ADHD symptoms: adult ADHD self-report scale § | 6.7 | 3.4 | |
| Paternal ADHD symptoms: adult ADHD self-report scale ¶ | 8.3 | 3.1 | |
| Maternal pre-pregnancy BMI (kg/m2) | 24.0 | 4.1 | |
| Paternal BMI (kg/m2) | 25.9 | 3.2 | |
| Child’s BMI at age 8 (kg/m2) | 16.3 | 2.0 | |
| Child depressive symptoms age 8: Short Mood and Feelings Questionnaire (SMFQ)** | 1.9 | 2.5 | |
| Child anxiety symptoms age 8: Screen for Child Anxiety Related Disorders (SCARED)†† | 1.0 | 1.2 | |
| Child ADHD symptoms age 8: Parent/Teacher Rating Scale for Disruptive Behaviour Disorders (RS-DBD) ‡ ‡ | 8.6 | 7.2 | |
| Child ADHD symptoms (inattention) age 8: Parent/Teacher Rating Scale for Disruptive Behaviour Disorders (RS-DBD) § § | 5.0 | 4.1 | |
| Child ADHD symptoms (hyperactivity) age 8: Parent/Teacher Rating Scale for Disruptive Behaviour Disorders (RS-DBD)§ § | 3.6 | 3.9 | |
| Categorical variables | Category | % | |
| Child’s sex | Male | 51.1 | |
| Female | 48.9 | ||
| Maternal educational qualifications | 9 year elementary education | 2.0 | |
| Up to 2 years further education | 4.1 | ||
| Further education: vocational | 12.2 | ||
| Further education: general studies, sixth form | 14.9 | ||
| Higher education: college/university, up to 4 years | 42.8 | ||
| Higher education: college/university, over 4 years | 24.0 | ||
| Paternal educational qualifications | 9 year elementary education | 3.4 | |
| Up to 2 years further education | 5.6 | ||
| Further education: vocational | 25.1 | ||
| Further education: general studies, sixth form | 12.9 | ||
| Higher education: college/university, up to 4 years | 28.4 | ||
| Higher education: college/university, over 4 years | 24.4 | ||
| Maternal parity at child’s birth | 0 | 46.8 | |
| 1 | 35.7 | ||
| 2 | 14.0 | ||
| 3+ | 2.7 | ||
| 4+ | 0.7 | ||
| Mother’s marital status at birth | Married/registered partner | 97.4 | |
| single | 2.6 | ||
| Mother’s smoking status during pregnancy | never | 51.0 | |
| Stopped before week 17 | 42.0 | ||
| Currently, sometimes | 2.4 | ||
| Currently, daily | 4.5 | ||
*
The reasons for exclusions and numbers in each case are shown in Appendix 1—figure 1. Missing data in BMI, outcomes and covariates was imputed using multiple imputation by chained equations. Descriptive statistics for the unimputed data are shown in Appendix 1.
†
Based on 5 items. Possible range: 0–15.
‡
Based on 8 items. Possible range: 0–24.
§
Possible range: 0–24.
¶
Possible range: 0–24.
**
Possible range: 0-26.
††
Possible range: 0–10.
‡ ‡
Possible range: 0–54.
§ §
Possible range: 0–27.