Table 2.

Explanation of features extracted from the HRCA signals

Domain	Signal feature	Significance
Time	Standard deviation	Reflects the signal variance around its mean value
	Skewness	Describes the asymmetry of amplitude distribution around mean
	Kurtosis	Describes the peakness of the distribution relative to normal distribution
Information-theoretic	Lempel–Ziv Complexity	Describes the randomness of the signal
	Entropy rate	Evaluates the degree of regularity of the signal distribution
Frequency	Peak frequency (Hz)	Describes the frequency of maximum power
	Spectral centroid (Hz)	Evaluates the median of the spectrum of the signal
	Bandwidth (Hz)	Describes the range of frequencies of the signal
Time–frequency	Wavelet entropy	Evaluates disorderly behavior for non-stationary signal