Table 2.

Detailed characteristics and formulas of feature.

Category	Num	Name	Formula
Time domain	1	Mean	$\mu =\frac{1}{N}{\displaystyle {\displaystyle \sum }_{i=1}^N}{x}_i$
	2	Variance	${\sigma }^2=\frac{1}{N}{\displaystyle {\displaystyle \sum }_{i=1}^N}{\left(x_i-\mu \right)}^2$
	3	Coefficient of variation	$cv=\frac{\left|\sigma \right|}{\mu }$
	4	Skewness	$s=\frac{\frac{1}{N}{{\displaystyle \sum }}_{i=1}^N{\left(x_i-\mu \right)}^3}{{\left(\frac{1}{N-1}{{\displaystyle \sum }}_{i=1}^N{\left(x_i-\mu \right)}^2\right)}^{3/2}}$
	5	Kurtosis	$k=\frac{\frac{1}{N}{{\displaystyle \sum }}_{i=1}^N{\left(x_i-\mu \right)}^4}{{\left(\frac{1}{N}{{\displaystyle \sum }}_{i=1}^N{\left(x_i-\mu \right)}^2\right)}^2}-3$
	6	IQR	$iqr=x_{sort}{}_{\left(N+1\right)\times 0.75}-x_{sort}{}_{\left(N+1\right)\times 0.25}$
	7	Activity	$act={\sigma }^2$
	8	Mobility	$mob=\sqrt{\frac{{\sigma }_{x^{\prime }}{}^2}{{\sigma }^2}}$
	9	Complexity	$com=\sqrt{\frac{{\sigma }_{x^{″}}{}^2/{\sigma }_{x^{\prime }}{}^2}{{\sigma }_{x^{\prime }}{}^2/{\sigma }^2}}$
	10	Zero-crossing	$ZC=\frac{1}{2}{\displaystyle {\displaystyle \sum }_{i=1}^N}\left|sgn\left(x_i\right)-sgn\left(x_{i-1}\right)\right|$
	11	Hurst	$H={\log }_N\left(C·E\left[\frac{\begin{array}{c}max\left(L_1,L_2,\cdots ,L_N\right)\\ -min\left(L_1,L_2,\cdots ,L_N\right)\end{array}}{\left|\sigma \right|}\right]\right),$ $L_i={{\displaystyle \sum }}_{i=1}^N(x_i-\mu )$
	12	DFA	$F\left(n\right)=\sqrt{\frac{1}{N}{\displaystyle {\displaystyle \sum }_{i=1}^N}{\left({\displaystyle {\displaystyle \sum }_{i=1}^N}(x_i-\mu )-y_n\left(i\right)\right)}^2}\propto n^{\alpha }$
Frequency domain	13	Sub-band power ratio (60–140 Hz/0–60 Hz)	$SPR=\frac{{{\displaystyle \int }}_{{\omega }_1}^{{\omega }_2}{s}_{xx}\left(\omega \right)d\omega }{{{\displaystyle \int }}_{{\omega }_2}^{{\omega }_3}{s}_{xx}\left(\omega \right)d\omega }$
	14	Power spectral density	$s_{xx}\left(\omega \right)=\underset{T\to \infty }{\lim }E\left[{\left|\widehat{X}\left(\omega \right)\right|}^2\right]$
	15	Amplitude spectral density	$\widehat{X}\left(\omega \right)=\frac{1}{\sqrt{T}}{{\displaystyle \int }}_0^{T}x\left(t\right)ex{p}^{-i\omega t}dt$
	16	Spectral centroid	$SC=\frac{{{\displaystyle \sum }}_{i=1}^N{f}_i·p\left(f_i\right)}{{{\displaystyle \sum }}_{i=1}^{N}p\left(f_i\right)}$
	17	Spectral kurtosis	$SK=\frac{{{\displaystyle \sum }}_{i=1}^N{\left(f_i-sc\right)}^{4}p\left(f_i\right)}{s{p}^4{{\displaystyle \sum }}_{i=1}^{N}p\left(f_i\right)}$
	18	Spectral entropy	$SE=\frac{-{{\displaystyle \sum }}_{i=1}^N{P}_i·\log P_i}{\log \left(length\left(P_i\right)\right)},P=\frac{x_i}{{{\displaystyle \sum }}_{i=1}^N{x}_i}$
TF domain	19–20	Fuzzy entropy	$FE=\ln O^m\left(m,r\right)-\ln O^{m+1}\left(m,r\right)$
Non-linear	21–25	Kraskov entropy	$\widehat{KE}\left(X\right)=-\phi \left(k\right)+\phi \left(N\right)+\log \left(V_d\right)$ $+\cdots \frac{d}{N}{\displaystyle {\displaystyle \sum }_{i=1}^N}\log \left(2\delta \left(x_i,k\right)\right),$ $V_d={\pi }^{d/2}/\mathsf{\Gamma }\left(1+d/2\right)/2^d,k=4$
	26–30	Renyi entropy	$R{E}_{\alpha }\left(X\right)=\frac{1}{1-\alpha }\log \left({\displaystyle {\displaystyle \sum }_{i=1}^N}{p}_i^{\alpha }\right),\alpha =2$
	31–35	Permutation entropy	$P{E}_D=-\frac{1}{{\log }_{2}D!}{\displaystyle {\displaystyle \sum }_{i=0}^{D!}}{p}_i{\log }_2{p}_i,D=3$
	36–40	Sample entropy	$SaE=-\ln \left[\frac{{\left(N-k+1\right)}^{-1}{{\displaystyle \sum }}_{i=1}^{N-k+1}{A}_i^k\left(r\right)}{{\left(N-m+1\right)}^{-1}{{\displaystyle \sum }}_{i=1}^{N-m+1}{B}_i^m\left(r\right)}\right],$ $m=2,r=0.2\times \left|\sigma \right|,k=m+1$
	41–45	Shannon entropy	$ShE\left(X\right)=\underset{\alpha \to 1}{\lim }R{E}_{\alpha }\left(X\right)=-{\displaystyle {\displaystyle \sum }_{i=1}^N}{p}_i\log p_i$
	46–50	Energy	$E={\displaystyle {\displaystyle \sum }_{i=1}^N}{x}_i{}^2$
	51–55	SVD Entropy	$Svd=-\frac{1}{\log \left(N\right)}{\displaystyle {\displaystyle \sum }_{j=1}^N}\left(\frac{s_j^2}{{{\displaystyle \sum }}_k{s}_k^2}\right)\log \left(\frac{s_j^2}{{{\displaystyle \sum }}_k{s}_k^2}\right)$
	56–60	PFD	$P_D=\frac{\log n}{\log n+\log \left(\frac{n}{n+0.4N}\right)}$
	61–65	KFD	$K_D=\frac{\log n}{\log \left(\frac{d}{L}\right)+\log n}$
	66–70	HFD	$H_D=\ln \left({\displaystyle {\displaystyle \sum }_{m=1}^k}{L}_m\left(k\right)\right)$

Note: TF: Time and frequency, IQR: Inter quartile range, DFA: Detrended fluctuation analysis, SVD: Singular value decomposition, PFD: Petrosian fractal dimension, KFD: Katz fractal dimension, HFD: Higuchi fractal dimension.