Table 1.

Tetrachoric correlation coefficients (r) and 95% confidence intervals (95% CI) for bulimia nervosa and alcohol use disorder.

			MZ	DZ
Within Trait	BN	N*	3768	2634
		Concordant/Discordant Pairs**	11 / 63	0 / 55
		r (95% CI)	0.63 (0.47; 0.79)	−0.02 (−0.47; 0.45)
	AUD	N*	4024	2860
		Concordant/Discordant Pairs*	55 / 175	20 / 141
		r (95% CI)	0.65 (0.57; 0.73)	0.42 (0.27; .056)
Cross Trait	Within Twin	N*	3942	2782
		Concordant/Discordant Diagnoses**	20 / 339	10 / 224
		r (95% CI)	0.30 (0.18; 0.42)	0.24 (0.08; 0.40)
	Cross Twin	N*	3882	2741
		Concordant/Discordant Pairs*	11 / 346	4 / 224
		r (95% CI)	0.14 (0.00; 0.28)	0.02 (−0.21; 0.23)

Note. N*= number of individuals used in the calculation

^*number of concordant affected pairs and number of discordant pairs used in the calculation

^**number of twins with both BN and AUD (concordant) and number of twins with only one diagnosis, BN or AUD (discordant). Within trait (“intraclass correlations”) correlations reflect the correlation of bulimia nervosa and alcohol use disorder between members of twin pairs by zygosity group. Cross-trait, within twin correlations reflect the correlation between bulimia nervosa and alcohol use disorder within individuals. Cross-trait, cross-twin correlations reflect the correlations of bulimia nervosa in one twin with alcohol use disorder in the co-twin by zygosity groups