The Kappa Coefficient and the Prevalence of a Diagnosis

Summary The kappa coefficient is a widely used measure of agreement between observers’ independent recording of diagnoses. Kappa adjusts the overall agreement for expected chance agreement. The dependence of kappa on the prevalence . of a diagnosis has not previously been emphasized. This dependence means that kappa does not give a general statement of the reproducibility of a diagnosis. The result of a study of observer agreement should, therefore, not – as it has been done in several studies – be given by the kappa value alone. The kappa value should always be given together with the original results of the study.