IQ was estimated with an abbreviated form of the WISCIIIUK,
a well-standardised assessment of full-scale, verbal,
and performance intelligence,26 which was given to 8-yearold
children at the ALSPAC research clinic with standard
neuropsy chological testing procedures.12 Suboptimum
cognitive outcomes were defined as the lowest 25% of
scores for full scale, verbal, and performance subscales.