ABSTRACT
The purpose of this chapter is to provide graphical examples of how multidimensional
item response theory (IRT) can be used by testing practitioners to better understand test
response data. The chapter begins with a review of the unidimensional IRT model from
both the factor-analytic perspective of McDonald (1999) and the traditional IRT approach
of Lord (1980). These approaches are then extended to the two-dimensional case.
Examples of how the two-dimensional model and corresponding graphical displays can
