linkage signal allowing for the objective evaluation of the linkage evidence. Second, the findings may not generalize to other large studies that were not ascertained for alcoholic probands. Third, only retrospective and cross-sectional data on cannabis use and use disorders were assessed. Fourth, comparisons to other large samples may be limited by differences in a number of genetic and environmentally determined variables. The exclusion criteria for this study eliminated participants reporting serious drug dependence on stimulants, cocaine, or opiates, current diagnosis of schizophrenia, bipolar disorder, or other psychiatric illness involving psychotic symptoms. This exclusion was included to create a more homogeneous sample for genetic analyses. However, this limitation reduces external validity and clinical applicability since the co-occurrence of mental health disorders and substance abuse is common. Additionally, this sample was comprised of almost entirely Caucasians that also limits applicability to other ethnic groups.
