Table 2.

Monozygotic (MZ) and dizygotic (DZ) twins: number of pairs and intra-class correlations.

	Mother		Father
	MZ n = 88	DZ n = 109	MZ n = 44	DZ n = 54
Effortful Control	.79	.43	.83	.59
Attentional Focusing	.57	−.02 ns	.39	−.19+
Inhibitory Control	.70	.24	.84	.43
Low-Intensity Pleasure	.86	.66	.84	.79
Perceptual Sensitivity	.72	.56	.83	.55
Surgency	.69	−.19	.41	−.51
Activity	.72	−.19	.47	−.39
High-Intensity Pleasure	.75	.06 ns	.51	−.26
Impulsivity	.45	−.13 ns	.07 ns	−.36
Shyness	.59	.11 ns	.63	−.02 ns
Negative Affectivity	.72	.34	.63	.63
Anger	.81	.47	.79	.50
Discomfort	.47	.03 ns	.39	.42
Soothability	.59	.23	.57	.38
Fear	.72	.47	.71	.36
Sadness	.69	.37	.64	.74
Other scales
Approach	.80	.39	.80	.35
Smiling	.66	.41	.72	.49

Note: all intra-class correlations significant (two-tailed p < .05) unless indicated,

⁺= p < .10 or “ns” = non-significant.