Table 5.

Concordance rates for ADHD in MZ and DZ twins (taken from Willcutt et al., 2010)

	Number of pairs		Probandwise concordance %
	MZ	DZ	MZ	DZ
Goodman & Stevenson (1989)	39	54	51	33
Levy et al. (1997)	57	46	82	38
Levy et al (2001)	138	109	67	42
Sherman et al (1997)	69	32	58	31
Thapar et al. (2001)	175*	410*	79	54
Todd et al. (2001)	72	135	68	22
Willcutt et al. (2000)	88	82	78	38
Willcutt et al. (2007)	83	78	68	24
Weighted average			71	41

^*specific Ns were not provided, so Ns are estimated based on the total sample and the 80^th percentile threshold were used to define ADHD probands.