A distinct lack of information on poly-substance use was conveyed by diversity of substances used in 11-year-olds (see Figure 2). Essentially, age 11 is too early to be able to reliably pinpoint an individual’s overall level of substance involvement. These substantial age-related differences in measure reliability are important to keep in mind, as studies of adolescent substance use tend to collapse across broad age bands (e.g. Maes et al., 1999; Rhee et al., 2003).
