Table 3.

Eight frequency domain statistical parameters ¹.

Domain	Indexes	Formula
Frequency	Mean of power spectrum Fmps	$F_{mps}={\displaystyle \sum _{j=1}^n{P}_j}/n$
	Root mean square of power spectrum Frms	$F_{rms}=\sqrt{{\displaystyle \sum _{j=1}^n{P}_j^2}/n}$
	Crest factor of power spectrum Fcf	$F_{cf}=\max \left\{\left|P_i\right|\right\}/F_{rms}$
	Modified equivalent bandwidth Fmeb	$F_{meb}=\sqrt{({\displaystyle \sum _{j=1}^n{(f_j-\overline{f})}^2{P}_j})/({\displaystyle \sum _{j=1}^n{P}_j})}$
	High–low ratio of power spectrum Fhlps	$F_{hlps}=({\displaystyle \sum _{j=n/4}^{n/2}{P}_i})/({\displaystyle \sum _{j=1}^{n/4}{P}_i})$
	Stabilization ratio Fsr	$F_{sr}=({\displaystyle \sum _{j=1}^n{f}_j^2{P}_i})/(\sqrt{{\displaystyle \sum _{j=1}^n{P}_i}}\sqrt{{\displaystyle \sum _{j=1}^n{f}_j^4{P}_i}})$
	Skewness of bandpower Fsb	$F_{sb}=({\displaystyle \sum _{j=1}^n{(P_i-F_{mps})}^3})/{({\displaystyle \sum _{j=1}^n{(P_i-F_{mps})}^2})}^{\frac{3}{4}}$
	Kurtosis of bandpower Fkb	$F_{sb}=n\cdot ({\displaystyle \sum _{j=1}^n{(P_i-F_{mps})}^4})/({\displaystyle \sum _{j=1}^n{(P_i-F_{mps})}^2})$

¹f_i is the frequency signal with x_i by FFT, P_i is the power spectrum of f_i, $\overline{f}=\sqrt{{\displaystyle \sum _{i=1}^n{f}_i^{}}/n}$.