| Sex | | |
| Male | | 3828 (50.8) |
| Female | | 3710 (49.2) |
| Missing | | 0 |
| Child’s ethnic background | | |
| White | | 6849 (90.0) |
| Non-white | | 290 (3.8) |
| Missing | | 399 (5.3) |
| Family history of strabismus/amblyopia | | |
| Yes | | 1209 (16.0) |
| No | | 6329 (84.0) |
| Missing | | 0 |
| Parental history of hypermetropia | | |
| Yes | | 632 (8.4) |
| No | | 6512 (86.4) |
| Missing | | 394 (5.2) |
| Parental social class (better of mother or her partner) | | |
| I | | 1078 (14.3) |
| II | | 3117 (41.4) |
| III (NM) | | 1723 (22.9) |
| III (M)/IV/V | | 1017 (13.5) |
| Missing | | 602 (8.0) |
| Type of housing (when child 8 months) | | |
| Owned/mortgaged | | 5869 (77.9) |
| Rented (subsidised) | | 671 (8.9) |
| Other rented + other | | 424 (5.6) |
| Missing | | 574 (7.6) |
| Mother smoked in first trimester | | |
| Yes | | 1382 (18.3) |
| No | | 5984 (79.4) |
| Missing | | 172 (2.3) |
| Mother smoked in last 2 weeks | | |
| Yes | | 1067 (14.2) |
| No | | 6297 (83.5) |
| Missing | | 172 (2.3) |
| Premature (gestation <37 weeks) | | |
| Yes | | 429 (5.7) |
| No | | 7109 (94.3) |
| Missing | | 0 |
| Intrauterine growth retardation (birth weight adjusted for gestation, >2 SD from the mean, that is <2307 g) | | |
| Yes | | 238 (3.2) |
| No | | 7212 (95.7) |
| Missing | | 88 (1.2) |