Table 2.

The mean and standard deviations and polychoric correlations of the four borderline personality disorder traits and five dimensions of the big five inventory in monozygotic and dizygotic (DZ) twin pairs

Zygosity	Variable	Mean*	Standard deviation*	Polychoric correlation†
Monosygotic	Affective instability	2.70	0.91	0.42
	Cognitive distortion	2.02	0.95	0.52
	Identity problems	2.13	0.85	0.52
	Insecure attachment	2.87	1.00	0.51
	Openness	3.61	0.68	0.64
	Conscientiousness	3.58	0.67	0.43
	Extraversion	3.25	0.88	0.48
	Agreeableness	3.82	0.62	0.45
	Neuroticism	2.96	0.76	0.46
DZ	Affective instability	2.80	1.00	0.18
	Cognitive distortion	2.11	1.05	0.29
	Identity problems	2.15	0.87	0.44
	Insecure attachment	2.71	1.01	0.11
	Openness	3.67	0.65	0.16
	Conscientiousness	3.61	0.75	0.29
	Extraversion	3.34	0.93	0.01
	Agreeableness	3.77	0.76	0.07
	Neuroticism	2.91	0.87	0.20

^*Mean and standard deviation computed using continuous variables.

^†Polychoric correlation computed using ordinal variables.