psychiatric and cannabis use history associated with cannabis withdrawal. We addressed these questions in two groups. The first included all frequent cannabis users in the survey (n=2,613), regardless of use of other substances. Results from this group maximized representativeness, but left the possibility open that withdrawal symptoms due to other substances were erroneously attributed to cannabis. The second group, a subset of the first (N=1,119), never abused other substances. This group served the important function of ensuring that results on withdrawal symptoms attributed to cannabis were not actually due to another substance.
