@article{covarianceandpcaforcategoricalvariables,
  title = {Covariance and PCA for Categorical Variables},
  author = {Hirotaka Niitsuma and Takashi Okada},
  year = {2007},
  eprint = {0711.4452},
  archivePrefix = {arXiv},
  url = {http://arxiv.org/abs/0711.4452v1},
}