Table 3.

Univariate, phenotypic and cross-trait cross-twin correlations on hyperactivity–impulsivity and inattention

	Hyperactivity–impulsivity	Inattention
Parent
MZ
Male	0.76 (0.70 to 0.81)	0.52 (0.42 to 0.61)
Female	0.75 (0.69 to 0.80)	0.59 (0.51 to 0.67)
DZ
Male	0.22 (0.10 to 0.38)	0.03 (−0.11 to 0.17)
Female	0.24 (0.10 to 0.38)	0.02 (−0.13 to 0.16)
DZ opposite-sex	0.14 (0.01 to 0.27)	0.04 (−0.10 to 0.17)

	Cross-trait phenotypic correlations	Cross-trait cross-twin correlations
MZ
Male	0.60 (0.52 to 0.68)	0.46 (0.36 to 0.56)
Female	0.58 (0.50 to 0.66)	0.46 (0.36 to 0.56)
DZ
Male	0.66 (0.58 to 0.74)	0.15 (0.01 to 0.29)
Female	0.50 (0.39 to 0.61)	0.13 (−0.02 to 0.27)
DZ opposite-sex	0.58 (0.48 to 0.66)	0.26 (0.13 to 0.39)

	Hyperactivity–impulsivity	Inattention
Teacher
MZ
Male	0.53 (0.43 to 0.62)	0.48 (0.37 to 0.58)
Female	0.60 (0.51 to 0.68)	0.68 (0.60 to 0.74)
DZ
Male	0.39 (0.25 to 0.52)	0.13 (−0.02 to 0.28)
Female	0.34 (0.19 to 0.48)	0.23 (0.07 to 0.38)
DZ opposite-sex	0.40 (0.27 to 0.52)	0.27 (0.12 to 0.40)

	Cross-trait phenotypic correlations	Cross-trait cross-twin correlations
MZ
Male	0.57 (0.47 to 0.65)	0.28 (0.15 to 0.40)
Female	0.36 (0.25 to 0.47)	0.23 (0.10 to 0.36)
DZ
Male	0.61 (0.50 to 0.69)	0.20 (0.05 to 0.35)
Female	0.45 (0.31 to 0.57)	0.13 (−0.04 to 0.28)
DZ opposite-sex	0.59 (0.49 to 0.67)	0.24 (0.10 to 0.40)

Phenotypic correlation, within-twin correlation of hyperactivity–impulsivity and inattentiveness; cross-trait cross-twin correlation, hyperactivity–impulsivity in Twin 1 correlated with inattentiveness in Twin 2