A remote data collection procedure was developed allowing for blood samples and other questionnaires to be returned by mail, and structured diagnostic interviews to be conducted by telephone, making nationwide data collection possible. Potential participants first had the study explained and gave written informed consent. A modified version of the Semi-Structured Assessment for the Genetics of Alcoholism (SSAGA) [Bucholz et al., 1994] was used to collect demographic, medical, psychiatric, alcohol, nicotine, cannabis, and other drug use history. The SSAGA is a fully structured, poly-diagnostic psychiatric interview that has undergone both reliability and validity testing. Modifications of the SSAGA for the present study included changes in diagnostic criteria and items to approximate DSM-IV criteria. Only the sections of the SSAGA relevant to substance abuse, demographics and medical history were utilized. We have previously demonstrated that a number of cannabis usage phenotypes are significantly heritable including: having ever used cannabis, used more than 21 times in a single year, DSM-IV cannabis dependence, individual criteria of DSM-IV cannabis dependence [Ehlers et al., unpublished work]. Two phenotypes with the highest heritability were cannabis “craving”
