An improved method of analysis of observer variation between pathologists

An improved method of analysing interobserver variation in histopathological studies is described and illustrated, by use of data from a congruence survey of malignant melanoma. The method provides, between any number of pathologists, an assessment of overall agreement and of agreement on each individual category of a classification system. Adjustment for differences in chance agreement due to varying numbers of categories or an altered composition of cases is included in the analysis. A generalization of the procedure designed to measure the strength of associations between different categories is formulated and explained with the use of an example.