Definition of accuracy and precision-evaluating CAS-systems

First CT-based navigation in ENT was established 20 years ago. Today, navigation systems display current 3D information of a pointing device within preoperatively generated volume CT scans. In the literature, the manufacturer's guide and protocols of certification we found divergent statements describing the accuracy of such systems, ranging from 1 to 9 mm. Often in an uncritical way, various variables are used in order to describe the accuracy. It seems to be obvious that straight criteria in evaluating navigational systems are missing. A unitary understanding for the term accuracy is non-existent in clinical practice. Furthermore, in the literature we found the incorrect equality for the terms precision and accuracy. The available literature on evaluating CAS-Systems was analysed. Then, the terms precision and accuracy were differentiated from established technical definitions. Using this perception, the term surgical accuracy was derived and suggested. In conclusion, the results were applied to our own study evaluating a navigation system. Precision is understood as the internal accuracy of measurements which is received through repeated measurements under equal conditions. It strongly depends on the sturdiness of the measuring instrument. In contrast, accuracy usually stands for an external accuracy under different circumstances. In metrology, the accuracy of measurements is affected by the impacts of all random components and systematic errors. From a technical and general perspective, accuracy is defined to be an approximation to a certain expected value. In a clinical setup it depends on the clinical requirements. The surgical accuracy of a navigation system should be informative about the maximum target positioning deviation, the arithmetic mean, the standard deviation and the number of measurements. An accepted reference value for deviation should be stated