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Journal of Mathematics
Volume 2014, Article ID 203907, 9 pages
http://dx.doi.org/10.1155/2014/203907
Research Article

New Interpretations of Cohen’s Kappa

Institute of Psychology, Unit Methodology and Statistics, Leiden University, P.O. Box 9555, 2300 RB Leiden, The Netherlands

Received 31 May 2014; Accepted 19 August 2014; Published 3 September 2014

Academic Editor: Yuehua Wu

Copyright © 2014 Matthijs J. Warrens. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Cohen’s kappa is a widely used association coefficient for summarizing interrater agreement on a nominal scale. Kappa reduces the ratings of the two observers to a single number. With three or more categories it is more informative to summarize the ratings by category coefficients that describe the information for each category separately. Examples of category coefficients are the sensitivity or specificity of a category or the Bloch-Kraemer weighted kappa. However, in many research studies one is often only interested in a single overall number that roughly summarizes the agreement. It is shown that both the overall observed agreement and Cohen’s kappa are weighted averages of various category coefficients and thus can be used to summarize these category coefficients.