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. 2017 Jul 4;17(7):1564. doi: 10.3390/s17071564

Table 2.

The statistical features in the time domain and frequency domain.

Feature Equation Feature Equation
Mean x1=1Ni=1Nxi Rectified mean x2=1Ni=1N|xi|
Peak to peak value x3=max(xi)min(xi) Root mean square x4=1Ni=1Nxi2
Standard deviation x5=i=1N(xix1)2N1 Skewness x6=i=1N(xix1)3(N1)x53
Kurtosis x7=i=1N(xix1)4(N1)x54 Impulse factor x8=max(xi)x2
Shape factor x9=x4x2 Crest factor x10=max(xi)x4
Coefficient of variation x11=x5x1 Mean frequency x12=k=1Ks(k)K
Frequency center x13=k=1Kfks(k)k=1Ks(k) Root mean square frequency x14=k=1Kfk2s(k)k=1Ks(k)
Standard deviation frequency x15=k=1K(fkxfc)2s(k)k=1Ks(k)

Note: xi is the ith value of signal x, N is the number of data points. s(k) is a spectrum for k=1,2,,K, K is the number of spectrum lines; fk is the frequency value of the kth spectrum line.