All diagnoses were made according to the DSM-IV criteria using the NIAAA Alcohol Use Disorder and Associated Disabilities Interview Schedule – DSM-IV version (AUDADIS) [19], which allows measurement of substance use and mental disorders in large-scale surveys. Detailed information on survey methods is described elsewhere [18]. Dependence diagnoses require the existence of 3 or more of the 7 DSM-IV diagnostic criteria within a 12 month period [20]. Age of dependence onset for each substance was defined as the age at which the respondent first met dependence diagnostic criteria for that particular substance.
