Sociodemographic characteristics of parents who opted out and who consented and were screened for eligibility
| Characteristic | Opted out (n=105)* | Consented and screened for eligibility (n=56) | t value, χ2 value | P value |
| Age, mean (SD, range) | 44.8 (7.6, 29–68) | 43.5 (7.2, 32–62) | −0.988 | 0.325 |
| Missing (n, %) | 19 (18.1) | 0 (0) | ||
| Gender (n, %) | ||||
| Female | 54 (51.4) | 33 (58.9) | 0.001 | 0.978 |
| Male | 38 (36.2) | 23 (41.1) | ||
| Missing | 13 (12.4) | 0 (0) | ||
| Relationship status (n, %) | ||||
| Partner | 86 (81.9) | 47 (83.9) | 1.996 | 0.158 |
| Single | 8 (7.6) | 9 (16.1) | ||
| Missing | 11 (10.5) | 0 (0) | ||
| If partner, cohabiting | ||||
| Yes | 78 (90.7) | 46 (97.9) | 1.035 | 0.309 |
| No | 5 (5.8) | 1 (2.1) | ||
| Missing | 3 (3.5) | 0 (0) | ||
| Level of education (n, %)† | ||||
| Lower secondary | 6 (5.7) | 1 (1.8) | 6.085 | 0.298 |
| Upper secondary | 30 (28.6) | 11 (19.6) | ||
| Post-secondary non-tertiary | 5 (4.8) | 3 (5.4) | ||
| Tertiary education | 50 (47.6) | 40 (71.4) | ||
| PhD | 2 (1.9) | 1 (1.8) | ||
| Not possible to categorise | 1 (1.0) | 0 (0) | ||
| Missing | 11 (10.5) | 0 (0) |
*One hundred and five parents who opted out provided some sociodemographic data. Sociodemographic characteristics were collected from parents who opted out by paper via the post (n=80) or Portal (n=24). One parent opted out via email and voluntarily provided some sociodemographic data.
†Level of education was self-reported as a free-text response, with responses categorised by the research team.