To cite gsbDesign in publications use:

Gerber F, Gsponer T (2016). “gsbDesign: An R Package for Evaluating the Operating Characteristics of a Group Sequential Bayesian Design.” Journal of Statistical Software, 69(11), 1–23. doi: 10.18637/jss.v069.i11.

Gsponer T, Gerber F, Bornkamp B, Ohlssen D, Vandemeulebroecke M, Schmidli H (2014). “A Practical Guide to Bayesian Group Sequential Designs.” Pharmaceutical Statistics, 13(1), 71–80. ISSN 1539-1612, doi: 10.1002/pst.1593.

Corresponding BibTeX entries:

  @Article{,
    title = {{gsbDesign}: An {R} Package for Evaluating the Operating
      Characteristics of a Group Sequential {B}ayesian Design},
    author = {Florian Gerber and Thomas Gsponer},
    journal = {Journal of Statistical Software},
    year = {2016},
    volume = {69},
    number = {11},
    pages = {1--23},
    doi = {10.18637/jss.v069.i11},
  }

  @Article{,
    title = {A Practical Guide to {B}ayesian Group Sequential Designs},
    author = {Thomas Gsponer and Florian Gerber and Bjorn Bornkamp and
      David Ohlssen and Marc Vandemeulebroecke and Heinz Schmidli},
    journal = {Pharmaceutical Statistics},
    year = {2014},
    volume = {13},
    number = {1},
    pages = {71--80},
    doi = {10.1002/pst.1593},
    issn = {1539-1612},
  }