To cite regDIF in publications use:

Belzak WCM (2021). regDIF: Regularized Differential Item Functioning. Duolingo, Pittsburgh, PA. version 1.0.0, https://github.com/wbelzak/regDIF/.

Corresponding BibTeX entry:

  @Manual{,
    title = {regDIF: Regularized Differential Item Functioning},
    author = {William C. M. Belzak},
    organization = {Duolingo},
    address = {Pittsburgh, PA},
    note = {version 1.0.0},
    year = {2021},
    url = {https://github.com/wbelzak/regDIF/},
  }