a 24 hour period). Alcohol problem measures included: The Mälmö-modified MAST (Mm-MAST;(17)), a 9-item self-report scale of drinking patterns and problems designed for application in Nordic cultures (18)) and the 22 items from the Rutgers Alcohol Problem Index (RAPI)(19), a reliable scale designed to assess problematic drinking. Parallel to current practice in gene identification efforts for alcohol dependence, only individuals who had evidence of alcohol exposure were included in twin analyses, so that genetic/environmental influences on the decision to initiate alcohol are not confounded with genetic/environmental influences on alcohol consumption or problems. Altogether 2% of the sample had never had a full alcoholic beverage and were excluded from analyses. All measures were coded so that higher scores indicated more frequent drinking or more drinking problems.
