There are certain considerations required in interpretation of this work. Firstly, analyses were conducted on retrospective self-report data, introducing the possibility of recall bias. This is a viable method of data collection (Darke, 1998; Sartor et al., 2011), and indeed recall of early experience with cannabis has been found to be especially reliable (Johnson and Mott, 2001), but as the analyses rely on accurate recall of age of onset of a number of behaviours the work would benefit from replication in longitudinal cohorts.
