To cite MPCI in publications use:

Edgar Santos-Fernandez, Michele Scagliarini (2012). MPCI: An R Package for Computing Multivariate Process Capability Indices. Journal of Statistical Software, 47(7), 1-15. URL http://www.jstatsoft.org/v47/i07/.

Corresponding BibTeX entry:

  @Article{,
    title = {{MPCI}: An {R} Package for Computing Multivariate Process
      Capability Indices},
    author = {Edgar Santos-Fern{\'a}ndez and Michele Scagliarini},
    journal = {Journal of Statistical Software},
    year = {2012},
    volume = {47},
    number = {7},
    pages = {1--15},
    url = {http://www.jstatsoft.org/v47/i07/},
  }