Table 1.

Demographic characteristics of the sex chromosome trisomies (SCT) and control group.

	SCT	Controls	Group differences
	n = 75	n = 81
Age in years – M (s.d.)	3.82 (1.90)	3.82 (1.60)	t(154) = 0.01, P = 0.992
Gender	M = 49, F = 26	M = 35, F = 46	X2(1) = 7.669, P = 0.006
Global intellectual functioning – M (s.d.)	97.34 (18.20)	108.11 (14.29)	t(136.39) = −4.052, P < 0.001
Range	59–138	72–140
Parental education level – median (range)	6 (4–7)	6 (2–7)	P = 0.794
Karyotype		N/A
47,XXX	26
47,XXY	39
47,XYY	10
Recruitment strategy – n (%)
Information-seeking parents	38 (50.7%)
Prospective follow-up	25 (33.3%)
Clinically referred	12 (16.0%)

For children aged 1.0–2.0, the Cognitive Composite score from the Bayley-3 (Bayley, 2006) was used as global intellectual functioning; for children aged 3.0 to 7–11, the estimated Full Scale IQ score from the short version of the WPPSI-III (Wechsler, 2002) was used as global intellectual functioning. Both scores have a mean of 100 and s.d. of 15.

SCT, sex chromosome trisomies.