Abstract
This study examined common and unique genetic and environmental influences on weekend drinking and weekday drinking reported by US male and female adult participants (mean age = 43.9). Data from 96 monozygotic and 82 dizygotic twin pairs were used to estimate bivariate biometric models of daily levels of weekend and weekday drinking volume. Weekend and weekday drinking volume scores were calculated from end-of-day reports of drinking across eight days. As expected, more drinking occurred during weekends. Biometric models provided evidence of significant additive genetic and nonshared environmental influences on both weekend and weekday drinking. Shared environmental influences were nonsignificant. Genetic influences accounted for a greater proportion of drinking variance during weekdays than weekends (0.36 compared to 0.17). However, these apparent differences in heritability-proportion of total variance accounted for by genetic variance-were due to increased nonshared environmental influences on weekend days, rather than greater genetic influences. The study's limitations are noted. Funded by National Institutes of Health/National Institute of Aging and John D. and Catherine T. MacArthur Foundation.