Table 6. Subgroup analysis of systemic error(mm) according to cervical spine level.

Variables	C1-2			C3-5			C6-7
	mean	SD	p-value	mean	SD	p-value	mean	SD	p-value
Translation
x	0.56	4.23	0.671	0.85	2.98	0.366	−0.07	2.35	0.922
y	2.88	11.8	0.436	1.9	11.60	0.598	−1.23	17.64	0.822
z	−0.18	1.09	0.595	−0.11	1.10	0.746	0	0.79	0.988
Rotation
x	−0.44	0.82	0.108	−0.07	0.36	0.509	−0.10	0.40	0.450
y	0.27	0.75	0.262	0.37	0.60	0.064	−0.02	0.36	0.861
z	−0.04	0.88	0.869	−0.31	0.37	0.020	−0.14	0.49	0.367