Get access

Chance-corrected measures for 2 × 2 tables that coincide with weighted kappa


Correspondence should be addressed to Matthijs J. Warrens, Institute of Psychology, Unit Methodology and Statistics, Leiden University, P.O. Box 9555, 2300 RB Leiden, The Netherlands (e-mail:


Cohen's kappa is presently a standard tool for the analysis of agreement in a 2 × 2 reliability study, and weighted kappa is a standard statistic for summarizing a 2 × 2 validity study. The special cases of weighted kappa, for example Cohen's kappa, are chance-corrected measures of association. For various measures of 2 × 2 association it has been observed in the literature that, after correction for chance, they coincide with a special case of weighted kappa. This paper presents the general function, linear in both numerator and denominator, that becomes weighted kappa after correction for chance.