Table 1 Distribution of variables used in the analysis (n = 7388)
Attributen (%)
Sex
    Male3828 (50.8)
    Female3710 (49.2)
    Missing0
Child’s ethnic background
    White6849 (90.0)
    Non-white290 (3.8)
    Missing399 (5.3)
Family history of strabismus/amblyopia
    Yes1209 (16.0)
    No6329 (84.0)
    Missing0
Parental history of hypermetropia
    Yes632 (8.4)
    No6512 (86.4)
    Missing394 (5.2)
Parental social class (better of mother or her partner)
    I1078 (14.3)
    II3117 (41.4)
    III (NM)1723 (22.9)
    III (M)/IV/V1017 (13.5)
    Missing602 (8.0)
Type of housing (when child 8 months)
    Owned/mortgaged5869 (77.9)
    Rented (subsidised)671 (8.9)
    Other rented + other424 (5.6)
    Missing574 (7.6)
Mother smoked in first trimester
    Yes1382 (18.3)
    No5984 (79.4)
    Missing172 (2.3)
Mother smoked in last 2 weeks
    Yes1067 (14.2)
    No6297 (83.5)
    Missing172 (2.3)
Premature (gestation <37 weeks)
    Yes429 (5.7)
    No7109 (94.3)
    Missing0
Intrauterine growth retardation (birth weight adjusted for gestation, >2 SD from the mean, that is <2307 g)
    Yes238 (3.2)
    No7212 (95.7)
    Missing88 (1.2)