Table 4.

Within-trait cross-twin and cross-trait cross-twin correlations.

		MZ correlation	DZ correlation
AGE 14 MONTHS
Within-trait	Restraint	0.28**	0.08
cross-twin	Toy removal	0.31**	0.19**
	Bayley scales	0.38**	−0.02
	Free play	0.25**	0.24*
Cross-trait	Restraint–Toy removal	0.11*	0.02
cross-twin	Restraint–Bayley scales	0.17**	0.17**
	Restraint–Free play	0.16**	0.06
	Toy removal–Bayley scales	0.18**	0.07
	Toy removal–Free play	0.18**	−0.03
	Bayley scales–Free play	0.15*	0.04
AGE 20 MONTHS
Within-trait	Restraint	0.50**	0.29**
cross-twin	Toy removal	0.29**	0.22**
	Bayley scales	0.34**	0.25**
	Free play	0.15	0.14
Cross-trait	Restraint–Toy removal	0.22**	0.04
cross-twin	Restraint–Bayley scales	0.09	0.12*
	Restraint–Free play	0.03	0.00
	Toy removal–Bayley scales	0.30**	0.20**
	Toy removal–Free play	0.07	0.13*
	Bayley scales–Free play	0.01	0.02
AGE 24 MONTHS
Within-trait	Restraint	0.52**	0.44**
cross-twin	Toy removal	0.30**	0.28**
	Bayley scales	0.35**	0.25*
	Free play	0.31**	0.26**
Cross-trait	Restraint–Toy removal	0.17**	0.17*
cross-twin	Restraint–Bayley scales	0.03	0.14*
	Restraint–Free play	0.15*	0.15*
	Toy removal–Bayley scales	0.17**	0.16*
	Toy removal–Free play	0.01	0.06
	Bayley scales–Free play	0.05	0.00

*p < 0.05; **p < 0.01.