Table 1.

Summary of 49 Bluetooth features used in this paper and their short descriptions.

Category	Abbreviation	Description	Number of features (N=49)
Statistical features	[Second-order feature]_[Daily feature], eg, Max_Mean	Second-order features (max, min, mean, and standard deviation) calculated in the PHQ-8a interval based on daily statistical Bluetooth features (max, min, mean, and standard deviation).	16
Multiscale entropy (MSE)	MSE_1, MSE_2, …, MSE_24	Multiscale entropy of the NBDCb sequences from scale 1 to scale 24.	24
Frequency domainc	LF_sum, MF_sum, HF_sum	The sums of spectrum power in LF, MF, and HF.	3
Frequency domain	LF_pct, MF_pct, HF_pct	The percentages of spectrum power in LF, MF, and HF to the total spectrum power.	3
Frequency domain	LF_se, MF_se, HF_se	Spectral entropy in LF, MF, and HF.	3

^aPHQ-8: 8-item Patient Health Questionnaire.

^bNBDC: nearby Bluetooth device count.

^cLF: low frequency (0-0.75 cycles/day); MF: middle frequency (0.75-1.25 cycles/day); HF: high frequency (>1.25 cycles/day).