The second set of analyses utilized LCA models. The LCA models were fitted to self-reported age of onset of tobacco, alcohol, cannabis, inhalants, and other substance. The models serve to investigate whether different groups exist in the sample regarding the pattern of drug use initiation. It is possible that groups have the same pattern of initiation and only differ with respect to mean age of onset (e.g., young age of onset vs. older age). It is also possible that groups differ with respect to initial drug preference such as early use of alcohol and tobacco but late onset of cannabis versus late onset of alcohol and tobacco but early onset of cannabis. How subjects are grouped in LCA is driven by the data. In the current analysis, only subjects who had reported use at some age were used in order to focus on differences between users, and to avoid bias due to right censoring. Right censoring is a form of missingness that is only taken into account in survival models. When fitting the latent class models, the ten SNPs on
