@article{CH97ml,
  author =	 "D.M. Chickering and D. Heckerman",
  Title =	 "Efficient approximations for the marginal likelihood
                  of {Bayesian} networks with hidden variables",
  journal =	 "Machine Learning",
  year =	 "1997",
  volume =	 "29",
  pages =	 "181-212"
}