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Kappa Coefficient

  1. Robert E. McGrath

Published Online: 30 JAN 2010

DOI: 10.1002/9780470479216.corpsy0484

Corsini Encyclopedia of Psychology

Corsini Encyclopedia of Psychology

How to Cite

McGrath, R. E. 2010. Kappa Coefficient. Corsini Encyclopedia of Psychology. 1.

Author Information

  1. Fairleigh Dickinson University

Publication History

  1. Published Online: 30 JAN 2010


The kappa coefficient was introduced by Cohen (1960) as a reliability statistic when two judges are classifying targets into categories on a nominal variable. It is most commonly used to estimate interrater reliability. Cohen (1968) later described weighted kappa, which considers degree of disagreement. For example, two judges classifying individuals on primary diagnosis could receive greater credit if they choose more rather than less similar diagnoses. Weighted kappa is particularly useful when categories are at least ordinally scaled. Another variant is available when there are more than two judges (Fleiss, 1981).


  • psychometric theory;
  • reliability;
  • intraclass correlation coefficient;
  • inter-rater reliability;
  • base rate;
  • proportion of agreement