@article{HawkingR03,
  author = {David Hawking and Stephen Robertson},
  title = {On Collection Size and Retrieval Effectiveness},
  journal = {Information Retrieval},
  year = {2003},
  volume = {6},
  number = {1},
  pages = {99--150},
  note = {\url{http://dx.doi.org/10.1023/A:1022904715765}}
}