TABLE 1

Correlates of Child IQ Levels at 8 Years Old

NTotal IQ ScoreP
MeanSD
Highest maternal educational achievement
    Degree level or “equivalent”a932115.615.1<.0001
    “Advanced” GCSE level or equivalent1492107.615.5
    “Ordinary” GCSE level or equivalent1991102.714.8
    Less than “ordinary” GCSE level or equivalent118596.915.0
Paternal social class
    Social class Ia669113.215.2<.0001
    Social class II1920107.716.1
    Social class III nonmanual643106.015.4
    Social class III manual1430100.714.8
    Social class IV/V52497.714.3
Housing tenure
    Secure (own home)4878105.816.1<.0001
    Insecure (rented, living with relatives or other)89398.616.0
Use of a car at birth
    Yesa5334105.216.1<.0001
    No37296.716.8
Infant parity (ordinal position):
    First borna2584106.316.0<.0001
    Second born2019104.716.3
    Third born718101.716.5
    Fourth born26799.915.5
Infant birth weight, g
    ≥4500a108105.918.0<.0001
    4000 to <4500a712105.315.8
    3000 to <4000a4115105.116.3
    2500 to <3000729102.616.0
    <250010796.415.9
Duration of breastfeeding, mo
    >6a1778109.116.3<.0001
    4 to 6901106.916.2
    0 to 31648103.415.7
    None104798.915.1
Child health in year before IQ measurement
    Rarely or sometimes illa5590104.816.2.001
    Often or always ill181100.617.5
Hospital admission over 8 y
    Nonea4273105.216.1.0002
    11044103.616.5
    2294103.016.7
    399101.916.3
    ≥46199.618.6
  • GCSE indicates General Certificate of Secondary Education.

  • a Reference group used in the multivariate analysis.