To cite lordif in publications, use:

  Choi, S. W., Gibbons, L. E., & 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), 1-30.
  https://doi.org/10.18637/jss.v039.i08

A BibTeX entry for LaTeX users is

  @Article{,
    title = {{lordif}: An R Package for Detecting Differential Item Functioning Using Iterative Hybrid Ordinal Logistic Regression/Item Response Theory and Monte Carlo Simulations},
    author = {Seung W. Choi and Laura E. Gibbons and Paul K. Crane},
    year = {2011},
    doi = {10.18637/jss.v039.i08},
    journal = {Journal of Statistical Software},
  }