To cite ssanv in publications use:

Fay, M.P.,Follmann, D.A., Halloran, M.E. (2007). Accounting for variability in sample size estimation with applications to nonadherence and estimation of variance and effect size Biometrics 63: 465--474.

Corresponding BibTeX entry:

  @Article{,
    title = {Accounting for variability in sample size estimation with
      applications to nonadherence and estimation of variance and
      effect size},
    author = {Michael P. Fay and M. Elizabeth Halloran and Dean A.
      Follmann},
    journal = {Biometrics},
    year = {2007},
    volume = {63},
    pages = {465--474},
  }