The tipping point: F-score as a function of the number of retrieved items

  • Authors:
  • Raf Guns;Christina Lioma;Birger Larsen

  • Affiliations:
  • University of Antwerp, IBW, Venusstraat 35, B-2000 Antwerpen, Belgium;University of Copenhagen, Department of Computer Science, Njalsgade 128, DK-2300 Copenhagen, Denmark;Royal School of Library and Information Science, Birketinget 6, DK-2300 Copenhagen S, Denmark

  • Venue:
  • Information Processing and Management: an International Journal
  • Year:
  • 2012

Quantified Score

Hi-index 0.00

Visualization

Abstract

One of the best known measures of information retrieval (IR) performance is the F-score, the harmonic mean of precision and recall. In this article we show that the curve of the F-score as a function of the number of retrieved items is always of the same shape: a fast concave increase to a maximum, followed by a slow decrease. In other words, there exists a single maximum, referred to as the tipping point, where the retrieval situation is 'ideal' in terms of the F-score. The tipping point thus indicates the optimal number of items to be retrieved, with more or less items resulting in a lower F-score. This empirical result is found in IR and link prediction experiments and can be partially explained theoretically, expanding on earlier results by Egghe. We discuss the implications and argue that, when comparing F-scores, one should compare the F-score curves' tipping points.