Table 2. Statistical analysis of positioning errors in X, Y and Z directions for three groups of targets.

Groups	X direction			Y direction			Z direction
	Z value	P value		Z value	P value		Z value	P value
Group A and Group B	−2.100	0.036		−1.775	0.076		−1.734	0.083
Group A and Group C	−3.306	0.001		−2.339	0.019		−1.783	0.075
Group B and Group C	−3.777	<0.001		−3.016	0.003		−2.789	0.005