Estimating Rater Agreement in 2 x 2 Tables: Correction for Chance and Intraclass Correlation

Abstract

Many estimators of the measure of agreement between two dichotomous ratings of a person have been proposed. The results of Fleiss (1975) are extended, and it is shown that four estimators— Scott's (1955) π coefficient, Cohen's (1960) k, Maxwell & Pilliner's (1968) r,,, and Mak's (1988) p—are interpretable both as chance-corrected measures of agreement and as intraclass correla tion coefficients for different ANOVA models. Rela tionships among these estimators are established for finite samples. Under Kraemer's (1979) model, it is shown that these estimators are equivalent in large samples, and that the equations for their large sample variances are equivalent.