To cite wnominate in publications use:

Keith Poole, Jeffrey Lewis, James Lo, Royce Carroll (2011). Scaling Roll Call Votes with wnominate in R. Journal of Statistical Software, 42(14), 1-21. URL http://www.jstatsoft.org/v42/i14/.

Corresponding BibTeX entry:

  @Article{,
    title = {Scaling Roll Call Votes with {wnominate} in {R}},
    author = {Keith Poole and Jeffrey Lewis and James Lo and Royce
      Carroll},
    journal = {Journal of Statistical Software},
    year = {2011},
    volume = {42},
    number = {14},
    pages = {1--21},
    url = {http://www.jstatsoft.org/v42/i14/},
  }