Baseline characteristics for parents/carers and young people according to experimental group
| Parent/carer baseline characteristics | Control (n=457) | SFP (intervention) (n=461) | |
| Age (median, IQR) | 37.0 (32.0–43.0) | 37.0 (33.0–42.5) | |
| Gender | Female | 105 (23.0%) | 103 (22.3%) |
| Male | 352 (77.0%) | 358 (77.7%) | |
| Ethnic group | White | 451 (98.7%) | 458 (99.6%) |
| Non-white | 6 (1.3%) | 2 (0.4%) | |
| Relationship status | Single, not in a relationship | 54 (12.0%) | 68 (14.8%) |
| Single, in a relationship | 97 (21.5%) | 91 (19.8%) | |
| Married/civil partnership | 200 (44.3%) | 183 (39.9%) | |
| Separated/divorced | 95 (21.1%) | 113 (24.6%) | |
| Widowed | 4 (0.9%) | 3 (0.7%) | |
| Other | 1 (0.2%) | 1 (0.2%) | |
| Ever smoked a cigarette | Never | 231 (50.5%) | 207 (44.9%) |
| Yes, at least once | 226 (49.5%) | 254 (55.1%) | |
| Ever drunk alcohol | Never | 85 (18.6%) | 90 (19.5%) |
| Yes, at least once | 372 (81.4%) | 371 (80.5%) | |
| AUDIT-C (Alcohol Use Disorder Identification Test for Consumption) | Low risk | 304 (66.5%) | 294 (64.6%) |
| High risk | 153 (33.5%) | 161 (35.4%) | |
| Ever taken drug | Never | 300 (65.6%) | 307 (66.6%) |
| Yes, at least once | 157 (34.4%) | 154 (33.4%) | |
| Deprivation overall score (median, IQR) | 27.5 (18.5–41.2) | 29.4 (18.0–44.5) | |
| Young people baseline characteristics | Control (n=454) | SFP (n=477) | |
| Age (median, IQR) | 11.5 (10.0–13.0) | 12.0 (11.0–13.0) | |
| Gender | Female | 231 (50.9%) | 269 (56.4%) |
| Male | 223 (49.1%) | 208 (43.6%) | |
| Ethnic group | White | 446 (98.5%) | 474 (99.6%) |
| Non-white | 7 (1.5%) | 2 (0.4%) | |
| Family affluence scale | Low (0–2) | 83 (18.4%) | 99 (20.9%) |
| Medium (3–5) | 234 (52.0%) | 231 (48.8%) | |
| High (6–9) | 133 (29.6%) | 143 (30.2%) | |
| Ever smoked a cigarette | Never | 330 (72.7%) | 348 (73.0%) |
| Yes, at least once | 124 (27.3%) | 129 (27.0%) | |
| Ever drunk alcohol | Never | 314 (69.3%) | 326 (68.5%) |
| Yes, at least once | 139 (30.7%) | 150 (31.5%) | |
| Ever taken drugs | Never | 433 (95.4%) | 450 (94.3%) |
| Yes, at least once | 21 (4.6%) | 27 (5.7%) | |
| Child deprivation overall score (median, IQR) | 28.1 (19.7–39.2) | 28.2 (18.3–39.6) | |
SFP, Strengthening Families Programme.