times in the previous year (Teesson et al., 2002), at least once a month for six months (Martin et al., 2006) or who reported using cannabis at lest five times during their lifetime (Langenbucher et al., 2004). In the other IRT study (Gillespie et al., 2007), individuals who endorsed using a drug six or more times in their lifetime but not 11 times in one month may have only been asked symptom items related to cannabis abuse, whereas those endorsing use 11 times in one month were asked all cannabis abuse and dependence criteria symptom items. As a result of these limitations, variability in cannabis use was restricted in all studies, and the use of consumption as a screen for cannabis dependence in one study (Gillespie et al., 2007) may have omitted numerous individual with dependence from the analysis. Third, except for the study by Teesson et al. (2002), previous studies conducted their psychometric analyses among lifetime cannabis users and examined lifetime endorsements of cannabis abuse and dependence criteria; lifetime measures are subject to recall bias.
