To cite superpc in publications use:

  Bair E. and Tibshirani R. (2004).  Semi-supervised methods to predict
  patient survival from gene expression data.  PLoS Biol.
  2004;2(4):e108.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {Semi-supervised methods to predict patient survival from gene expression data},
    author = {E. Bair and R. Tibshirani},
    journal = {PLoS Biol},
    year = {2004},
    volume = {2},
    number = {4},
    pages = {e108},
  }

  Bair E., Hastie T., Paul D., and Tibshirani R. (2006).  Prediction by
  supervised principal components.  J. Am. Stat. Assoc.
  2006;101(473):119-137.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {Prediction by supervised principal components},
    author = {E. Bair and T. Hastie and D. Paul and R. Tibshirani},
    journal = {J. Am. Stat. Assoc.},
    year = {2006},
    volume = {101},
    number = {473},
    pages = {119-137},
  }