For tobacco, alcohol, and cannabis, the survival mixture Model M2C2 was the best fitting model according to all fit indices. The M2C2 model discriminates between long-term survivors (i.e., zero risk of onset), and subjects who reported an age of first use or might engage in use in the future. The class proportion of the users class were similar for tobacco and alcohol (0.45 and 0.49, respectively), and smaller in the case of cannabis (0.26). In the case of tobacco and alcohol, the class proportions were somewhat higher than the reported first use, showing that this class contains a small proportion subjects who, based on their higher similarity in the covariates with the users, are considered to be potential future users. The class proportion of cannabis reflects the reported first use. There were no sex differences between the classes in either one of these three phenotypes.
