Coefficients for interrater agreement

The degree of agreement between two raters who rate a number of objects on a certain characteristic can be expressed by means of an association coefficient (e.g., the product-moment correlation). A large number of association coefficients have been proposed, many of which belong to the class of Euclidean coefficients (ECs). A discussion of desirable properties of ECs demonstrates how the identity coefficient and its generalizations, which constitute a family of ECs, can be used to assess interrater agreement. This family of ECs contains coefficients for both nominal and non-nominal (ordinal and metric) data. In particular, it is pointed out which information contained in the data is accounted for by the various coefficients and which information is ignored. Index terms: association coefficients, correlation, Euclidean coefficients, generalized identity coefficients, interrater agreement