To cite package 'longpower' in publications use:

Michael C Donohue, Steven D Edland (2016). longpower: Power and sample size calculators for longitudinal data. R package version 1.0-16.

Diggle PJ, Heagerty PJ, Liang K, Zeger SL. Analysis of longitudinal data. Second Edition. Oxford Statistical Science Serires. 2002.

Liu, G., & Liang, K. Y. (1997). Sample size calculations for studies with correlated observations. Biometrics, 53(3), 937-47.

Corresponding BibTeX entries:

  @Manual{,
    title = {longpower: Power and sample size calculators for linear
      mixed models},
    author = {Michael C. Donohue and Anthony C. Gamst and Steven D.
      Edland},
    year = {2016},
    note = {R package version 1.0-16},
  }

  @Book{,
    title = {Analysis of longitudinal data},
    author = {P. J. Diggle and P. J. Heagerty and K. Y. Liang and S. L.
      Zeger},
    year = {2002},
    edition = {Second Edition},
    publisher = {Oxford Statistical Science Serires},
  }

  @Article{,
    title = {Sample size calculations for studies with correlated
      observations},
    author = {G. Liu and K. Y. Liang},
    year = {1997},
    journal = {Biometrics},
    volume = {53(3)},
    pages = {937-47},
  }