The Kappa Statistic: A Second Look
In recent years, the kappa coefficient of agreement has become the de facto standard for evaluating intercoder agreement for tagging tasks. In this squib, we highlight issues that affect kappa and that the community has largely neglected. First, we discuss the assumptions underlying different computations of the expected agreement component of kappa. Second, we discuss how prevalence and bias affect the K measure.
Di Eugenio, B. and Glass, Michael, "The Kappa Statistic: A Second Look" (2004). Mathematics and Computer Science Faculty Publications. Paper 18.