Item Response Theory

In this chapter, the two basic assumptions of IRT (i.e., unidimensionality and local independence), the three most commonly used dichotomous IRT models (i.e., 1PLM, 2PLM, and 3PLM), and the three most commonly applied or cited polytomous IRT models (GRM, PCM, and GPCM) are introduced. At the same time, the calculation methods of item and test information for dichotomous and polytomous IRT models are described.