All analyses were conducted in Stata statistical software version 11 (StataCorp, 2009). Two separate Cox proportional hazard models were fitted to the data to test the association between a number of potential associated factors and speed of progression from (1) birth to opportunity to use cannabis and (2) opportunity to use cannabis to the development of cannabis dependence. Both were assessed as time in years. Details of the two Cox Proportional Hazards models are provided below:
