Fig. 4

Graphic illustration of the target point deviation. Box and whisker plots displaying the target point deviation of all target points in mm using the frameless optical neuronavigation system. The whiskers represent minimum and maximum values, the black line inside each box the median value and lower and upper box boundaries 25th and 75th percentiles, respectively. (A) Target point deviation of all 50 predetermined target points read out by two observers (total, n = 100) and for both observers separately (n = 50). (B) Target point deviation divided in groups depending on affiliation of access to the cerebrum (frontal bone and parietal bone, n = 64), cerebellum (occipital bone, n = 16) and pituitary fossa (basisphenoidal bone, n = 20)