To cite geepack in publications use:

Halekoh U, Højsgaard S, Yan J (2006). “The R Package geepack for Generalized Estimating Equations.” Journal of Statistical Software, 15/2, 1–11.

Yan J, Fine JP (2004). “Estimating Equations for Association Structures.” Statistics in Medicine, 23, 859–880.

Yan J (2002). “geepack: Yet Another Package for Generalized Estimating Equations.” R-News, 2/3, 12–14.

Corresponding BibTeX entries:

  @Article{,
    title = {The R Package geepack for Generalized Estimating
      Equations},
    author = {Ulrich Halekoh and Søren Højsgaard and Jun Yan},
    year = {2006},
    journal = {Journal of Statistical Software},
    volume = {15/2},
    pages = {1--11},
  }

  @Article{,
    title = {Estimating Equations for Association Structures},
    author = {Jun Yan and Jason P. Fine},
    year = {2004},
    journal = {Statistics in Medicine},
    volume = {23},
    pages = {859--880},
  }

  @Article{,
    title = {geepack: Yet Another Package for Generalized Estimating
      Equations},
    author = {Jun Yan},
    year = {2002},
    journal = {R-News},
    volume = {2/3},
    pages = {12--14},
  }