Table 4.

Heritabilities and genetic correlations (95% confidence intervals) from the best-fitting bivariate models of vocabulary and three separate alcohol problem measures

	Vocabulary	RAPI	Max drinks	AD symptoms
Heritability	0.72 (0.61–0.79)	0.60 (0.46–0.71)	0.56 (0.44–0.66)	0.54 (0.41–0.65)
Genetic correlation	1	−0.31 (−0.44 to −0.18)	−0.29 (−0.43 to −0.16)	−0.20 (−0.34 to −0.06)

RAPI, Rutgers Alcohol Problem Index ; Max drinks, maximum number of drinks consumed in a 24-h period ; AD, alcohol dependence.

To reduce skewness, RAPI and AD symptoms were Box–Cox transformed and Max drinks square root transformed.

In all models, different means for monozygotic (MZ) and dizygotic (DZ) twins were estimated and sex was included as a covariate.

The estimates are from bivariate AE models with only genetic covariance in the model.