Item response theory (IRT) is a general framework for specifying mathematical functions that describe the interactions of persons and test items. It has a long history, but its popularity is generally attributed to the work of Fredrick Lord and Georg Rasch starting in the 1950s and 1960s. Multidimensional item response the- ory (MIRT) is a special case of IRT that is built on the premise that the mathematical function includes as parameters a vector of multiple person characteristics that de- scribe the skills and knowledge that the person brings to a test and a vector of item characteristics that describes the difficulty of the test item and.
