## 3 Data Analysis
### Gait Features Extraction
Regarding Walk Ratio, literature findings suggest that when comparing results from normal to slow walking speeds, increased values are expected, something that was also observed for all groups of participants when examining the mTUG to WST-Slow test, while when examining WST- Normal to Slow test it is noted only in the case of EL group (for S and PD groups values are concentrated around the same level), possibly due to the smaller differences of gait velocity between different tests, below 0.3 m/s [54; 55]. Moreover, in each test, PD patients had the lowest results regarding step and stride length, gait velocity, and step frequency while they had the highest results on the number of steps. The percentages of the stance and swing phases, which in a normal gait cycle are expected to be 60% and 40%, respectively, are met in most cases with a slight deviation from 0.5-1.5%. All of these observations are in line with literature findings [31; 54; 55; 56; 57]. Subsequently, in order to examine the effect of ON and OFF medication states on the performance of PD participants regarding their spatial and temporal gait characteristics, we have extracted gait-related features for both medication states, as shown in Table 6. In general, the behavior of the features exploring the different walking speeds is in line with the previously described findings shown in Table 4. Regarding the ON and OFF phases, we observe an increase of values in steps number, double support (%), and step frequency features, and a decrease in step and stride duration, swing time, single support (%) and Walk Ratio, features, in ON phase. Gait velocity does not appear to have a notable effect in the ON phase, for all tests. Step and stride length slightly decrease in the WST-Normal and High tests for the ON phase, while they remain at the same level in WST-Slow and mTUG tests. Subsequently, we separated the PD participants according to their disease severity levels based on their ratings on MDS-UPDRS-Part III, by applying the cut-off values described in Section 2.4; the relevant results are presented in Table 6. We should point out that there are no recordings in the severe level as rated by the MDS-UPDRS-Part III. Although we did record a PD patient (PD015) classified as severe PD, we had to exclude the recordings because he needed support to perform the WST-High and the mTUG tests and therefore his weight distribution and pressure factors were affected. Examining the results for normal pace of walking, from mild to moderate levels we observe that as the severity of the disease increases, single support (%), swing phase (%), Walk Ratio, spatial and spatiotemporal characteristics decrease, while all the rest increase. These observations are also met in the case of WST-Slow with the difference that swing time decreases. For WST-High, features behavior differentiate from WST-Normal observations in moderate severity with the swing time, single support (%), and swing phase (%) to increase, while with the double support time, the double support (%), and the stance phase (%) to decrease. Regarding Walk Ratio, we observe that on moderate severity levels it is, in all tests, decreased (spanning from 5.09 \(\pm\) 1.17 to 5.41 \(\pm\) 1.39), which agrees with literature findings in pathological gait, 5.36 \(\pm\) 0.86, Ref. [53], in comparison with mild severity levels (spanning from 6.63 \(\pm\) 1.62 to 6.78 \(\pm\) 1.43), which overlaps with literature on normal gait of healthy adults (6.5 \(\pm\) 0.8) [53]. Therefore, the results indicate that as the severity level increases, the Walk Ratio decreases, however, for mild stages of the disease it may not be indicative. In what follows we focus on feature selection techniques to reveal the dominant features for model training, which are described in Section 3.2; the results of which are presented in Section 4. In so doing, we also take into consideration literature findings regarding the importance of a deeper study of the ON/OFF medication states and disease severity levels [17; 31; 48].