Due to the large number of comparisons calculated (N=210), an alpha level of 0.001 was used for all significance testing. Figure 1 contains graphical plots derived from these parameter estimates. Looking across various substances in Table 3 and Figure 1, the substances maintained a reasonably consistent rank-ordering in terms of location. Alcohol tended to be at the low end, as indicated by its Item Response Functions (IRFs) and Item Information Functions (IIFs) being located farther left on the Figure (indicating that lower trait severity was required for likely endorsement of use). By contrast, the other controlled substances item indicated the greatest severity (as illustrated by its IRFs being located farthest to the right on the Z-score trait scale in Figure 1).
