No significant substance-level sex effects were observed in discriminations (see Table 3), nor were any consistent trends apparent. Specific substance locations reported in Table 3 also did not differ significantly between males and females, with the exception of tobacco at age 14 having a greater (more severe) location for females than males. However, Figure 1 illustrates a general trend for all substances to be more severe (i.e. their IRF midpoints and IIF peaks were located farther right) for females than males across ages. This means that, within an age group, a female must have a higher trait level on the underlying dimension of poly-substance use to endorse having used the same substances as a male. Because the sex difference trend in severity is consistent across substances, it may be thought of as impacting the underlying dimension, rather than acting in a specific way on distinct substances. Although there are not significant differences at the level of specific substances, equating parameters across sex diminished model fit, as shown in Table 2, suggesting a broader generalized influence of sex on poly-substance use.
