Global and partial agreement among several observers.

The advantage of modelling agreement on a categorical scale among observers rather than using summarizing indices is now well established. However, analysis of agreement among more than two observers is essentially based on pairs of observers. We present a global and partial agreement modelling approach derived from the quasi-independence and quasi-symmetry log-linear models. This approach addresses high order interactions in the contingency table rather than two-way interaction in the pairwise agreement approach. Pairwise, global and partial agreement models were applied to the detection by six pathologists of three lesions in biopsy specimens arising from patients suspected to be affected by Crohn's disease. The global and partial agreement approach surpasses the pairwise agreement approach, especially if there is heterogeneity among ratings.