Comparisons between those who did and did not report lifetime cannabis use opportunity, and those who did and did not progress to cannabis use following opportunity, show these groups differ on the majority of the covariates tested within the survival models (see Table 1 and 2). Mean age of first cannabis use opportunity was 17.6 (s.d. 3.2) and the mean age of cannabis dependence 21.4 (s.d. 4.1). The mean survival time for the participants in the cannabis use opportunity model was 19.1 years (s.d. 5.1) (age at opportunity, or for those who did not report opportunity, age at interview. This figure is higher than the mean opportunity age as individuals who have not experienced opportunity by the point of interview are also included in the survival model, with their age at time of interview in place of age of opportunity). The mean survival time for participants in the cannabis dependence model was 13.4 years (s.d. 4.9) (time from opportunity to dependence, or for those who did not develop dependence, time from opportunity to age at interview). This figure is higher
