Choi, S. W., Gibbons, L. E. and Crane, P. K. (2011) “lordif: An R Package for Detecting Differential Item Functioning Using Iterative Hybrid Ordinal Logistic Regression/Item Response Theory and Monte Carlo Simulations”, Journal of Statistical Software, 39(8), pp. 1–30. doi: 10.18637/jss.v039.i08.