To further investigate the relationship of abuse and dependence criteria, the work group and other researchers used item response theory analysis, which builds on factor analysis, to better understand how items (in this case, the criteria) relate to each other. Item response theory models indicate criterion severity (inversely related to frequency: rarely endorsed criteria are considered more severe) and discrimination (how well the criterion differentiates between respondents with high and low severity of the condition). The results from these analyses are often presented graphically (Figure 2), where each curve represents a criterion. Curves toward the right indicate criteria of greater severity; steeper slopes indicate better discrimination (see Table S2 in the online data supplement for more detail about Figure 2).
