Table 1.

Twin correlations for psychopathic personality traits, internalizing, and externalizing

	Men		Women		Combined
	MZ (95% CI)	DZ (95% CI)	MZ (95% CI)	DZ (95% CI)	MZ (95% CI)	DZ (95% CI)
Fearless Dominance	0.42 (0.29–0.54)	0.20 (−0.01 to 0.40)	0.45 (0.34–0.56)	0.21 (0.02 to 0.39)	0.44 (0.36–0.52)	0.20 (0.06–0.34)
Impulsive Antisociality	0.51 (0.39–0.61)	0.17 (−0.05 to 0.38)	0.49 (0.37–0.59)	0.28 (0.10 to 0.44)	0.50 (0.41–0.57)	0.24 (0.10–0.37)
Internalizing	0.48 (0.34–0.59)	0.19 (−0.04 to 0.40)	0.29 (0.17–0.41)	0.14 (−0.05 to 0.32)	0.35 (0.25–0.44)	0.15 (0.01–0.29)
Externalizing	0.70 (0.62–0.77)	0.44 (0.27 to 0.59)	0.68 (0.60–0.74)	0.26 (0.08 to 0.42)	0.68 (0.63–0.73)	0.37 (0.25–0.48)

MZ, Monozygotic twins; DZ, Dizygotic twins; CI, confidence interval.

All twin correlations were estimated by fitting models to the raw data using maximum-likelihood estimation, which corrects for any potential biases due to missing data. n=1252 individuals from 626 twin pairs, some with missing data. Internalizing was calculated by taking the average standardized (via z-score transformation) symptom count score among major depression, social phobia, and simple phobia. Externalizing was calculated in the same manner using symptoms of adult antisocial behavior, conduct disorder, and alcohol, nicotine, and drug dependence. Combined refers to models in which parameters were equated across the genders.