results were less clear in males: an equally good fit was found for models in which 24% and 61% of variance was accounted for by genetic factors. In a longitudinal study by King et al. (2005), heavy drinking was assessed at ages 17 and 20 and heritability in females was estimated at 18% and 30%, respectively; for males heritability was 57% at age 17 and 39% at age 20.
