TABLE 2.

Summary of descriptive statistics for the confounders

Confounder	Controls	Cases
Biological sex
Male (49.0%)	3096 (48.4%)	169 (64.3%)
Female (51.0%) p < 0.001	3303 (51.6%)	94 (35.7%)
Maternal education
<O level (21.7%)	1265 (21.4%)	70 (28.9%)
O level a (35.2%)	2093 (35.3%)	79 (32.6%)
A levels b or higher (38.4%) p = 0.019	2566 (43.3%)	93 (38.4%)
Performance IQ
Mean (sd) p = 0.009	107.2 (16.6%)	101.0 (18.9%)
Verbal IQ
Mean (sd) p = 0.038	99.8 (17.0%)	93.9 (19.0%)
Total IQ
Mean (sd) p = 0.003	104.3 (16.3%)	97.6 (18.9%)

Abbreviation: IQ, intelligence quotient.

^a Compulsory examssinations taken at age 16.

^b Optional examinations taken at age 18.