In this section, the **data** set of joints and COP in AP from a typical subject is evaluated by the determinism test and stationarity test.  Figures 2(a), 2(c), 2(e), and 2(g). This clearly confirms the deterministic nature of human balance system. The average cross-prediction error for all possible combinations of and is given in Figures 2(b), 2(d), 2(f), and 2(h). The average values of all are 0.1839, 0.2215, 0.1398, and 0.8951 (for the time series of hip, knee, ankle, and COP in AP, resp.). Since each maximal cross-prediction error is not significantly larger than the average, the studied time series are clearly stationary.