Table 1 Correlation coefficients for the relationship of IQ at 7, 9 and 11 years with social and physical characteristics of study participants.

	IQ at 7 years	IQ at 9 years	IQ at 11 years
Birth weight
r	0.11	0.09	0.09
n	6905	6803	6813
Father's social class in childhood†
r	−0.31	−0.29	−0.31
n	6905	6803	6813
Family size in childhood†
r	−0.24	−0.21	−0.24
n	6898	6774	6807
Housing tenure in childhood
r	0.24	0.23	0.22
n	6873	6774	6783
Car ownership in childhood
rpb*	0.17	0.15	0.15
n	6860	6760	6768
Educational attainment
r	0.52	0.56	0.61
n	6812	6711	6721
Income in adulthood
r	0.29	0.30	0.32
n	6756	6656	6667
Social class in adulthood†
r	−0.40	−0.43	−0.46
n	6752	6657	6672
Housing tenure in adulthood
r	0.23	0.22	0.24
n	6895	6793	6803
Car ownership in adulthood
r	0.21	0.19	0.19
n	6892	6790	6768

*Point biserial correlation coefficient.

†Higher scores on these variables indicates greater socioeconomic adversity.

For all correlation coefficients, p<0.001.