TABLE 2.

Associations Between Confounding Variables and Psychotic Symptoms at Age 12 in a Twin Cohort (N=2,127)

Confounding Variable	Group				Relative Risk	95% CI
	No Definite Psychotic Symptoms (N=2,002)		At Least One Definite Psychotic Symptom (N=125)
	N	%	N	%
Individual and socioeconomic factors
Male	963	48.10	71	56.80	1.39	0.95–2.03
Socioeconomic deprivationa	658	32.87	53	42.40	2.33	1.38–3.91
	Mean	SD	Mean	SD
IQ	100.53	14.89	93.02	14.60	0.97	0.96–0.98
Psychopathologyb
Internalizing problems	12.00	8.23	14.25	9.63	1.03	1.01–1.04
Externalizing problems	18.08	13.58	22.76	15.64	1.02	1.01–1.03
	N	%	N	%
Genetic vulnerabilities
Mothers with psychosis syndrome	99	5.08	14	11.67	2.28	1.25–4.18
Genetic composite riskc
Low	858	42.86	49	39.20	1.35	0.90–2.02
High	48	2.40	14	11.20	5.62	2.85–11.12
Highest	44	2.20	18	14.40	7.23	3.66–14.31

^aConstructed from a standardized composite of income, parents’ education, and social class.

^bInternalizing and externalizing problems were assessed at age 5 using the Child Behavior Checklist (for mothers) and the Teacher’s Report Form (for teachers). Scores represent summed subscales from the two instruments, as described in the text.

^cThe target twin’s genetic risk was coded as “low” when the dizygotic co-twin did not report any definite psychotic symptoms; “high” when the dizygotic co-twin reported at least one definite symptom; and “highest” when the monozygotic co-twin reported at least one definite symptom. All groups were compared with the group that had the “lowest” genetic risk, that is, when the target twin’s monozygotic co-twin did not report any psychotic symptoms.