Inverse Document Frequency (IDF): A Measure of Deviations from Poisson

  • K. Church
  • W. Gale
Part of the Text, Speech and Language Technology book series (TLTB, volume 11)


Low frequency words tend to be rich in content, and vice versa. But not all equally frequent words are equally meaningful. We will use inverse document frequency (IDF), a quantity borrowed from Information Retrieval, to distinguish words like somewhat and boycott. Both somewhat and boycott appeared approximately 1000 times in a corpus of 1989 Associated Press articles, but boycott is a better keyword because its IDF is farther from what would be expected by chance (Poisson).


Information Retrieval Word Frequency Hide Variable Inverse Document Frequency Poisson Mixture 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© Springer Science+Business Media Dordrecht 1999

Authors and Affiliations

  • K. Church
  • W. Gale

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