Table 5.

Repeated-measures correlations among the final set of features calculated during the 24 hours of the day when participants answered the surveys and 95% CI (N=14,695 observations from 657 participants).

Measures	Correlations, rrm (95% CI)
	SDNNa	RMSSDb	MRRIc	PNN50d	SDANNe	Triangular index	LFf/HFg	Total power	VLFh
SDNN	—i	—	—	—	—	—	—	—	—
RMSSD	0.2 (0.19 to 0.22)	—	—	—	—	—	—	—	—
MRRI	0.27 (0.25 to 0.28)	0.49 (0.48 to 0.51)	—	—	—	—	—	—	—
PNN50	0.21 (0.19 to 0.23)	0.93 (0.93 to 0.93)	0.45 (0.43 to 0.46)	—	—	—	—	—	—
SDANN	0.82 (0.81 to 0.82)	0.02 (0 to 0.03)	0.02 (0 to 0.04)	0.04 (0.03 to 0.06)	—	—	—	—	—
Triangular index	0.67 (0.66 to 0.68)	0.26 (0.24 to 0.27)	0.29 (0.28 to 0.31)	0.3 (0.29 to 0.32)	0.5 (0.49 to 0.51)	—	—	—	—
LF/HF	0.24 (0.23 to 0.26)	−0.33 (−0.34 to −0.31)	0.33 (0.31 to 0.34)	−0.35 (−0.37 to −0.34)	0.17 (0.15 to 0.18)	0.14 (0.12 to 0.16)	—	—	—
Total power	0.36 (0.35 to 0.38)	0.84 (0.83 to 0.84)	0.62 (0.61 to 0.63)	0.84 (0.84 to 0.84)	0.13 (0.11 to 0.14)	0.37 (0.36 to 0.38)	0.01 (−0.01 to 0.03)	—	—
VLF	0.42 (0.41 to 0.44)	0.69 (0.68 to 0.7)	0.63 (0.62 to 0.64)	0.68 (0.67 to 0.69)	0.18 (0.17 to 0.2)	0.39 (0.37 to 0.4)	0.15 (0.14 to 0.17)	0.94 (0.94 to 0.95)	—
SD2/SD1	0.69 (0.68 to 0.7)	−0.5 (−0.52 to −0.49)	−0.14 (−0.16 to −0.13)	−0.48 (−0.5 to −0.47)	0.67 (0.66 to 0.68)	0.37 (0.35 to 0.38)	0.47 (0.46 to 0.48)	−0.29 (−0.3 to −0.27)	−0.14 (−0.16 to −0.13)

^aSDNN: SD of normal-to-normal intervals.

^bRMSSD: root mean square of successive differences.

^cMRRI: mean RR interval.

^dPNN50: proportion of normal-to-normal intervals that differ by >50 milliseconds.

^eSDANN: SD of the averages of normal-to-normal intervals.

^fLF: low frequency.

^gHF: high frequency.

^hVLF: very low frequency.

ⁱUpper triangle of the correlation matrix was omitted for simplicity and readability.