To cite shrink in publications use:

Daniela Dunkler, Willi Sauerbrei, Georg Heinze (2016). Global, Parameterwise and Joint Shrinkage Factor Estimation. Journal of Statistical Software, 69(8), 1-19.<doi:10.18637/jss.v069.i08>

Corresponding BibTeX entry:

  @Article{,
    title = {Global, Parameterwise and Joint Shrinkage Factor
      Estimation},
    author = {Daniela Dunkler and Willi Sauerbrei and Georg Heinze},
    journal = {Journal of Statistical Software},
    year = {2016},
    volume = {69},
    number = {8},
    pages = {1--19},
    doi = {10.18637/jss.v069.i08},
  }