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Table 2 Analysis of the computed features from the displacement of the COP.

From: Study of age-related changes in postural control during quiet standing through Linear Discriminant Analysis

  Young Adult (Groups 1 and 2) Elderly Adult (Groups 6 and 7) ANOVA p-value Correlation with age Correlation Groups
Features OE CE OE CE OE CE OE CE  
Mean Velocity 6.15 9.45 8.27 14.52 <   r = 0.3 r = 0.28  
Ap (mm/s) * ± 1.32 ± 3.08 ± 3.69 ± 10.74 0.03     A
Mean Velocity 5.40 7.54 7.14 12.91 < < r = 0.25 r = 0.29  
Ml (mm/s) * ± 1.05 ± 2.77 ± 3.35 ± 9.15 0.04 0.02    B
Mean Velocity 9.11 13.45 12.12 21.55 < < r = 0.29 r = 0.29  
RD (mm/s) * ± 1.59 ± 4.05 ± 5.43 ± 15.63 0.03 0.04    C
Range 21.10 27.84 18.62 27.90    r = -0.03 r = -0.07  
Ap (mm) ± 5.57 ± 8.03 ± 4.74 ± 10.80      D
Range 19.80 21.59 20.37 24.53    r = -0.05 r = 0.02  
Ml (mm) ± 6.40 ± 7.32 ± 7.98 ± 10.43      E
Displacement 230.6 320.0 299.3 500.2 < < r = 0.27 r = 0.28  
Ap (mm) * ± 47.7 ± 90.7 ± 118.8 ± 369.2 0.03 0.05    A
Displacement 171.4 235.8 229.4 414.7 < < r = 0.28 r = 0.3  
Ml (mm) * ± 30.8 ± 81.6 ± 102.1 ± 300.6 0.03 0.02    B
Displacement 273.4 403.6 363.7 646.7 < < r = 0.29 r = 0.29  
RD (mm) * ± 47.6 ± 121.4 ± 163.0 ± 469.2 0.03 0.04    C
RMS 4.52 5.74 3.60 4.91    r = 0.42 r = 0.48  
Ap (mm) ± 1.52 ± 1.82 ± 0.94 ± 1.95    p < 0.01 p < 0.001 F
RMS 4.04 4.27 3.79 4.57    r = 0.33 r = 0.44  
Ml (mm) ± 1.39 ± 1.47 ± 1.22 ± 1.82     p < 0.001 G
Mean Freq. 0.21 0.25 0.33 0.42 < < r = 0.41 r = 0.51  
Ap (Hz) * ± 0.06 ± 0.07 ± 0.16 ± 0.19 0.01 0.001 p < 0.01 p < 0.001 F, H
Mean Freq. 0.22 0.28 0.30 0.41 < < r = 0.34 r = 0.46  
Ml (Hz) * ± 0.07 ± 0.06 ± 0.08 ± 0.12 0.01 0.001 p < 0.01 p < 0.001 G, I
Peak Freq. 0.05 0.08 0.09 0.19    r = 0.27 r = 0.28  
Ap (Hz) ± 0.03 ± 0.06 ± 0.07 ± 0.24      
Peak Freq. 0.06 0.10 0.07 0.15    r = 0.13 r = 0.25  
Ml (Hz) ± 0.03 ± 0.07 ± 0.05 ± 0.09      
F50 0.083 0.13 0.20 0.27 < < r = 0.43 r = 0.48  
Ap (Hz) * ± 0.03 ± 0.05 ± 0.14 ± 0.18 0.01 0.01 p < 0.001 p < 0.001 H
F50 0.11 0.16 0.17 0.28 < < r = 0.28 r = 0.45  
Ml (Hz) * ± 0.05 ± 0.05 ± 0.10 ± 0.12 0.04 0.001   p < 0.001 I
F80 0.25 0.34 0.46 0.63 < < r = -0.29 r = -0.22  
Ap (Hz) * ± 0.11 ± 0.12 ± 0.26 ± 0.33 0.01 0.001    D
F80 0.30 0.36 0.40 0.59 < < r = -0.14 r = -0.05  
Ml (Hz) * ± 0.11 ± 0.08 ± 0.14 ± 0.23 0.03 0.001    E
Total Power 23.99 38.40 14.35 28.14    r = -0.28 r = -0.2  
Ap ± 17.88 ± 25.04 ± 7.44 ± 23.95      D
Total Power 19.20 21.44 16.44 24.57    r = -0.16 r = -0.05  
Ml ± 12.80 ± 14.53 ± 10.54 ± 19.45      E
Conf. Ellipse 223.0 325.5 172.6 305.3    r = -0.23 r = -0.14  
area (mm2) ± 128.9 ± 210.4 ± 93.0 ± 249.5      J
Conf. Ellipse 10.77 12.29 8.79 11.02    r = -0.31 r = -0.2  
major axis (mm) ± 3.29 ± 3.69 ± 2.48 ± 4.11      D, J
Conf. Ellipse 1.97 1.78 2.16 2.20   < r = 0.09 r = 0.31  
angle (rad)* ± 0.38 ± 0.36 ± 0.58 ± 0.40   0.01    
SDA - Ds 0.13 0.33 0.21 0.69    r = 0.21 r = 0.24  
Ap ± 0.06 ± 0.21 ± 0.18 ± 0.89      A
SDA - Ds 0.12 0.23 0.21 0.58 < < r = 0.26 r = 0.3  
Ml * ± 0.04 ± 0.16 ± 0.17 ± 0.57 0.04 0.01    B
SDA - Dl 0.05 0.05 0.02 0.02 <   r = -0.27 r = -0.23  
Ap * ± 0.04 ± 0.05 ± 0.02 ± 0.04 0.04     
SDA - Dl 0.03 0.02 0.02 0.02    r = -0.16 r = -0.09  
Ml ± 0.02 ± 0.03 ± 0.02 ± 0.02      
SDA - Hs 1.81 1.78 1.74 1.76 <   r = -0.31 r = -0.16  
Ap * ± 0.06 ± 0.04 ± 0.08 ± 0.06 0.01     
SDA - Hs 1.80 1.77 1.77 1.78    r = -0.11 r = 0.03  
Ml ± 0.05 ± 0.05 ± 0.05 ± 0.06      
SDA - Hl 0.64 0.44 0.32 0.23 < < r = -0.44 r = -0.44  
Ap * ± 0.22 ± 0.19 ± 0.24 ± 0.17 0.001 0.01 p < 0.001 p < 0.001  
SDA - Hl 0.44 0.30 0.33 0.21    r = -0.23 r = -0.18  
Ml ± 0.20 ± 0.13 ± 0.17 ± 0.13      
SDA-critical time 1.08 1.31 1.04 0.95   < r = -0.1 r = -0.38  
Ap (s) * ± 0.51 ± 0.31 ± 0.41 ± 0.42   0.01   p < 0.01  
SDA-critical time 1.43 1.28 1.25 0.98   < r = -0.19 r = -0.38  
Ml (s) * ± 0.78 ± 0.33 ± 0.32 ± 0.27   0.01   p < 0.01  
SDA (mm2) 0.16 0.41 0.17 0.43    r = -0.03 r = -0.02  
critical mag.-Ap ± 0.14 ± 0.27 ± 0.09 ± 0.31      
SDA (mm2) 0.21 0.30 0.21 0.38    r = -0.08 r = 0.01  
critical mag.-Ml ± 0.18 ± 0.22 ± 0.13 ± 0.27      
DFA - α 1.43 1.57 1.49 1.62    r = 0.16 r = 0.12  
Ap ± 0.09 ± 0.09 ± 0.13 ± 0.16      
DFA - α 1.72 1.78 1.70 1.81    r = -0.09 r = 0.01  
Ml ± 0.06 ± 0.09 ± 0.12 ± 0.12      
H R/S 0.97 1.01 0.99 1.02    r = 0.2 r = 0.04  
Ap ± 0.04 ± 0.02 ± 0.03 ± 0.02      
H R/S 1.03 1.03 1.02 1.03    r = -0.09 r = -0.01  
Ml ± 0.004 ± 0.005 ± 0.01 ± 0.01      
ApEn 0.008 0.008 0.010 0.012 < < r = 0.24 r = 0.43  
Ap * ± 0.002 ± 0.002 ± 0.003 ± 0.005 0.05 0.01   p < 0.001  
ApEn 0.007 0.009 0.008 0.011   < r = 0.14 r = 0.29  
Ml * ± 0.002 ± 0.002 ± 0.002 ± 0.003   0.01    
  1. Note that OE is the experimental condition of opened eyes whereas CE is the closed eyes. The mean and standard deviation are presented for each feature. Features that presented a significant difference between the groups are highlighted with '*' and in this case the estimated p-value of the ANOVA is shown. The correlation between the age and the feature is also presented. In the last column we present the analysis of the correlation between the studied features. When a correlation coefficient larger than 0.9 was found the features were included in the same group labeled by letters A, B, C, D, E, F, G, H, I, J.