If you use exams()/exams2pdf() please cite:

Bettina Gruen, Achim Zeileis (2009). Automatic Generation of Exams in R. Journal of Statistical Software 29(10), 1-14. URL http://www.jstatsoft.org/v29/i10/.

If you use any other exams2xyz() interface, please cite:

Achim Zeileis, Nikolaus Umlauf, Friedrich Leisch (2012). Flexible Generation of E-Learning Exams in R: Moodle Quizzes, OLAT Assessments, and Beyond. Journal of Statistical Software 58(1), 1-36. URL http://www.jstatsoft.org/v58/i01/.

Corresponding BibTeX entries:

  @Article{,
    title = {Automatic Generation of Exams in {R}},
    author = {Bettina Gr\"un and Achim Zeileis},
    journal = {Journal of Statistical Software},
    year = {2009},
    volume = {29},
    number = {10},
    pages = {1--14},
    url = {http://www.jstatsoft.org/v29/i10/},
  }
  @Article{,
    title = {Flexible Generation of E-Learning Exams in {R}: {Moodle}
      Quizzes, {OLAT} Assessments, and Beyond},
    author = {Achim Zeileis and Nikolaus Umlauf and Friedrich Leisch},
    journal = {Journal of Statistical Software},
    year = {2014},
    volume = {58},
    number = {1},
    pages = {1--36},
    url = {http://www.jstatsoft.org/v58/i01/},
  }