To cite lordif in publications use:

Seung W. Choi, Laura E. Gibbons, Paul K. Crane (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. URL http://www.jstatsoft.org/v39/i08/.

Corresponding BibTeX entry:

  @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},
    journal = {Journal of Statistical Software},
    year = {2011},
    volume = {39},
    number = {8},
    pages = {1--30},
    url = {http://www.jstatsoft.org/v39/i08/},
  }