To cite interval in publications use:

Michael P. Fay, Pamela A. Shaw (2010). Exact and Asymptotic Weighted Logrank Tests for Interval Censored Data: The interval R Package. Journal of Statistical Software, 36(2), 1-34. URL http://www.jstatsoft.org/v36/i02/.

Corresponding BibTeX entry:

  @Article{,
    title = {Exact and Asymptotic Weighted Logrank Tests for Interval
      Censored Data: The {interval} {R} Package},
    author = {Michael P. Fay and Pamela A. Shaw},
    journal = {Journal of Statistical Software},
    year = {2010},
    volume = {36},
    number = {2},
    pages = {1--34},
    url = {http://www.jstatsoft.org/v36/i02/},
  }