Fig. 5. Agreement statistics (A , raw agreement; B , kappa; C , phi) for contrast dye distribution stratified by level (point estimates [blobs ] and 95% CI [whiskers ]). Accuracy of contrast dye distribution varied between the different levels: it was significantly worse at the medial branch of C7, whereas all other levels showed very good accuracy. Formal statistical significance for differences among levels was reached only for the raw agreement statistic (P value for interaction <0.001, whereas P value for interaction = 0.124 for κ statistics and P = 0.127 for φ). TON = third occipital nerve.