IRT (item response theory) models Item response theory using Stata: One-parameter logistic (1PL) models Item response theory using Stata: Two-parameter logistic (2PL) models Item response theory using Stata: Three-parameter logistic (3PL) models Item response theory using Stata: Nominal response (NRM) models Item response theory using Stata: Rating scale (RSM) models Item response theory using Stata: Graded response (GRM) models