While previous studies examined age and sex effects on overall substance use in the context of disordered use (Kirisci et al., 2006) and adult use (Kirisci et al., 2002), an IRT framework has not yet been applied to examine both developmental and sex effects on poly-substance use in a longitudinal, community-based adolescent sample. This is an important gap in the literature because adolescence is the period most critical to understanding the emergence of substance use. To fill this gap, the present study aimed to understand how specific substances relate to an underlying dimension of poly-substance use involvement, and whether use of different substances is well-conceptualized as a single latent trait. We examined interpretations of the use of substances between age and sex groups, as well as the ways in which age and sex affect the structure and information provided by the poly-substance use dimension.
