Efforts are under way to improve existing DSM-IV criteria for cannabis use disorders, e.g. by the addition of withdrawal as a dependence criterion [142]. Quantitative assessments of liability to cannabis use disorders (e.g. cannabis abuse/dependence symptom counts) may also enhance statistical power for gene association studies. For example, there is overwhelming support for a unidimensional factor underlying DSM-IV cannabis abuse and dependence criteria [143-146]. Utilization of a factor score generated using the abuse and dependence symptoms would allow investigators to assess the role of genotype across a range of liability. Such quantitative measures, particularly those using factor analytic approaches, can incorporate additional measures of cannabis use (e.g. frequency or duration use, withdrawal) and also be used to identify cases and controls based on high or low scores on this liability spectrum.
