Fleiss Kappa Calculator

Fleiss' kappa is a summary statistic for the level of agreement among a fixed number of raters when assigning categorical ratings to a set of items. This tool computes the classic unweighted Fleiss' kappa from an n x k rating matrix, where n is the number of subjects and k is the number of categories. The calculation relies on the per-subject category counts n_ij and the total number of raters per subject. It produces P_bar, the mean agreement, and P_bar_e, the chance agreement based on category frequencies, then yields kappa = (P_bar - P_bar_e) / (1 - P_bar_e). The tool validates that each row sums to the same number of raters and that all counts are non-negative integers.