To cite PerFit in publications use:

Tendeiro JN, Meijer RR, Niessen ASM (2016). “PerFit: An R Package for Person-Fit Analysis in IRT.” Journal of Statistical Software, 74(5), 1–27. doi:10.18637/jss.v074.i05.

Corresponding BibTeX entry:

  @Article{,
    title = {{PerFit}: An {R} Package for Person-Fit Analysis in
      {IRT}},
    author = {Jorge N. Tendeiro and Rob R. Meijer and A. Susan M.
      Niessen},
    journal = {Journal of Statistical Software},
    year = {2016},
    volume = {74},
    number = {5},
    pages = {1--27},
    doi = {10.18637/jss.v074.i05},
  }