Table 1.

Descriptive Statistics for Time-Constant Characteristics

Variable
Outcome
NVQ level, %
Level 1	13.93
Level 2	31.02
Level 3	19.34
Level 4	32.10
Level 5	3.61
Time-constant characteristics
Male	46.83
Mother’s age at birth	27.63
Maternal grandfather’s social class	Skilled manual/nonmanual
Age mother finished schooling	15–16 years old
Age father finished schooling	15–16 years old
Monthly Family income	184.41
Mother’s marital status at birth	97.50
Mother’s smoking status
Nonsmoker	69.52
Medium smoker	13.89
Heavy smoker	11.03
Variable smoker	5.56
Breastfed as infanta	71.00
Both parents presenta	86.78
Child’s post-school expectations, %b
Get a job	18.17
Continue full-time education	30.02
Not sure	51.81
Average number of O-levelsc	2.12
N	4,644

^ais considered as a time-constant covariate after birth.

^bis considered as a time-constant covariate after age 7.

^cis considered as a time-constant covariate after age 11.