Table 3.

Twin correlations for the completion times of each of the three cards and the interference score (95% confidence interval in brackets).

Zygosity	N Twin1	N Twin2	Card 1	Card 2	Card 3	Interference score (3 minus 2)
MZM	32	33	0.68 (0.45 – 0.83)	0.78 (0.60 – 0.88)	0.75 (0.55 – 0.87)	0.44 (0.12 – 0.68)
DZM	23	22	0.41 (0.02 – 0.69)	0.47 (0.08 – 0.74)	0.37 (-0.03 – 0.67)	0.11 (-0.30 – 0.49)
MZF	43	43	0.70 (0.51 – 0.82)	0.60 (0.36 – 0.76)	0.70 (0.51 – 0.83)	0.55 (0.29 – 0.73)
DZF	16	16	0.25 (-0.24 – 0.64)	0.38 (-0.10 – 0.72)	0.68 (0.32 – 0.87)	0.32 (-0.17 – 0.68)
DOS	27	26	0.29 (-0.08 – 0.60)	0.31 (-0.07 – 0.61)	0.19 (-0.18 – 0.52)	0.10 (-0.28 – 0.46)

Note: MZM = monozygotic males; DZM = dizygotic males; MFZ = monozygotic females; DZF = dizygotic females; DOS = opposite sex pairs. N Twin 1 is the number of first born twins per zygosity group; N Twin 2 is the number of second born twins.