Encyclopedia of Database Systems

2009 Edition
| Editors: LING LIU, M. TAMER ÖZSU

Precision at n

  • Nick Craswell
Reference work entry
DOI: https://doi.org/10.1007/978-0-387-39940-9_484

Synonyms

 P@n

Definition

In an information retrieval system that retrieves a ranked list, the top-n documents are the first n in the ranking. Precision at n is the proportion of the top-n documents that are relevant.

Key Points

If r relevant documents have been retrieved at rank n, then:
$${\rm{\ Precision\ at\ n}} =\, {{r}\over {n}}$$
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Copyright information

© Springer Science+Business Media, LLC 2009

Authors and Affiliations

  • Nick Craswell
    • 1
  1. 1.Microsoft Research CambridgeCambridgeUK