Table 1.

Spectral features used for OSA severity classification. S1DT = stage-one decision tree; S2LR = stage-two linear regression model.

Feature	Frequency Sub-Band	Statistic Calculated from Fast Fourier Transform (FFT) Coefficients	Classification Stage
X[1]	0.06–0.08 Hz	kurtosis	S1DT
X[2]	0.36–0.38 Hz	skewness	S2LR
X[3]	0.96–0.98 Hz	skewness	S2LR
X[4]	1.18–1.20 Hz	kurtosis	S1DT
X[5]	1.40–1.42 Hz	kurtosis	S2LR
X[6]	1.68–1.70 Hz	skewness	S1DT