Table 2.

Interobserver agreement (Cohen’s kappa coefficient) of tested classification systems

Classification	M1	M2 (Rosenberg et al. 1988)	M3 (Conti et al. 1992)	M4 (Kong and Van Der Vliet 2008)
Intraoperative findings
OP1–OP2	0.59	0.72	0.60	0.59
Preoperative MRI findings
MR1–MR2	0.48	0.39	0.32	0.52
Intraoperative–preoperative findings
OP1–MR1	−0.05	0.30	0.07	0.30
OP1–MR2	0.10	0.32	0.24	0.32
OP2–MR1	0.05	0.43	0.17	0.30
OP2–MR2	0.21	0.28	0.18	0.38
OP–MR (mean kappa coefficient, 95 % CI)	0.08 (0.05–0.10)	0.33 (0.32–0.35)	0.17 (0.15–0.18)	0.33 (0.32–0.33)