To cite ssanv in publications use:

Fay MP, Halloran ME, Follmann DA (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},
  }