In the present article we reported only single trajectories from univariate longitudinal analyses, conducted for the different risk behaviors. However, risk behaviors tend to co-occur, which is not accounted for in this article. One further limitation is that the growth models assume that a single growth trajectory with a common starting or end point can adequately represent growth in the whole sample. Individual variation around the average trajectory, which might be important in understanding these processes for different individuals or groups, is not of interest in such modeling. Also, our primarily descriptive study does not seek to analyze predictors of the observed population trajectories. A more clinical perspective focuses on the differential vulnerability of individuals for engaging in risk behaviors and tries to identify subgroups with distinct trajectories as well as distinct explanatory variables for each subgroup. Mixture models covering different forms of risk behaviors may be more appropriate for a clinical or etiological approach, and it is our intention to explore those as a next step. Despite these shortcomings, growth models are useful for epidemiological purposes or population-based prevention,
