Accuracy and precision are important concepts for understanding how an eye tracker performs, and how can one evaluate the quality of the recorded eye tracking data.
During data collection, accuracy and precision are used as indicators of the eye tracker data validity. A system with good accuracy and precision will provide more valid data as it is able to truthfully describe the location of a person’s gaze on a screen. Accuracy is deﬁned as the average difference between the real stimuli position and the measured gaze position. Precision is deﬁned as the ability of the eye tracker to reliably reproduce the same gaze point measurement, i.e. it measures the variation of the recorded data via the Root Mean Square (RMS) of successive samples.
The required level of accuracy and precision depends on the nature of the eye tracking study. Small uncertainties, for instance, can be critical when analyzing gaze data in reading studies or studies with a small stimulus.
The accuracy error varies considerably across participants and experimental conditions. Accuracy is dependent on participant properties, illumination in the test environment, stimuli properties, calibration quality, data collection procedure and the eyes’ position in the track box.