Latent class models for 2–5 classes were fitted to first use of alcohol, tobacco, cannabis, inhalants, and other substances. The 3-class model had the lowest BIC, whereas the the 4-class model had the lowest AIC and saBIC, which has a less severe correction for sample size than the standard BIC. Importantly, in both models, the classes were ordered with respect to onset. This means that the subjects in the Add Health sample can best be grouped with respect to an early onset class, one or two medium onset classes, and a late onset class. The 5-class model had one empty class and resembled the 4-class model with respect to the non-empty classes. The 5-class model is therefore not further considered.
