To cite growcurves in publications use:

Terrance D. Savitsky, Susan M. Paddock (2014). Bayesian Semi- and Non-Parametric Models for Longitudinal Data with Multiple Membership Effects in R. Journal of Statistical Software, 57(3), 1-35. URL http://www.jstatsoft.org/v57/i03/.

Corresponding BibTeX entry:

  @Article{,
    title = {{B}ayesian Semi- and Non-Parametric Models for
      Longitudinal Data with Multiple Membership Effects in {R}},
    author = {Terrance D. Savitsky and Susan M. Paddock},
    journal = {Journal of Statistical Software},
    year = {2014},
    volume = {57},
    number = {3},
    pages = {1--35},
    url = {http://www.jstatsoft.org/v57/i03/},
  }