Finger tapping movements (open-close movements of thumb and index finger) are routinely tested in order to evaluate motor function of Parkinson's disease (PD) patients, and more than ten different indices calculated from measured data have been used in medical diagnosis. However, underlying relationships among the indices and even basic factors influencing them remain still unknown. This paper investigates the basic factors that influence the motor function evaluation of the finger tapping movements and proposes a novel method to classify and evaluate the movements of the normal elderly subjects and the PD patients based on the extracted features of abnormal movements. In the experiments, finger tapping movements of 35 PD patients and 86 normal elderlies were evaluated based on 12 indices, and the factor analysis was applied to the results. The results indicate the finger movements of PD patients have three factors: opening and closing ability of fingers; stability of the movements; and movement rhythm. Also, it can be observed that the subjects can be classified into eight groups by thresholding the three factors. The results lead us to conclude that the factor analysis enables the detailed investigation of the motor function by classifying the subject movements.
