Table 2.

Correlation coefficient of HRV metrics by the interpolation method.

Domain	HRV metric	Non-interpolated	Interpolation method
			NNI	LI	CSI
Time	AVNN	0.920 (41.6%)	–	–	–
	SDNN	0.994 (0.2%)	0.997 (2.0%)	0.993 (3.0%)	0.993 (2.4%)
	SDSD	0.986 (0.1%)	0.998 (2.2%)	0.983 (3.6%)	0.994 (3.3%)
	RMSSD	0.986 (0.1%)	0.998 (2.2%)	0.983 (3.6%)	0.994 (3.3%)
	pNN50	0.999 (4.9%)	–	0.986 (31.8%)	0.992 (22.1%)
Frequency	TP	0.992 (0.2%)	0.993 (2.4%)	0.981 (3.0%)	0.991 (2.4%)
	VLF	0.971 (0.7%)	0.948 (4.9%)	0.988 (4.5%)	0.974 (4.0%)
	LF	0.985 (0.2%)	0.978 (2.0%)	0.968 (2.3%)	0.985 (1.9%)
	HF	0.995 (0.1%)	0.998 (1.8%)	0.993 (3.0%)	0.997 (2.2%)
	LF/HF	0.837 (0.3%)	0.234 (14.3%)	0.652 (6.3%)	0.604 (6.3%)
	nLF	–	0.786 (8.3%)	0.905 (5.1%)	0.898 (5.1%)
	nHF	0.887 (0.2%)	0.995 (0.1%)	0.991 (0.1%)	0.993 (0.1%)
Non-linear	SD1	0.932 (0.1%)	0.998 (1.1%)	0.986 (1.9%)	0.995 (1.7%)
	SD2	0.994 (0.3%)	0.997 (2.4%)	0.981 (3.0%)	0.995 (2.4%)
	ApEn	0.889 (0.2%)	0.872 (2.5%)	0.838 (3.3%)	0.847 (3.0%)

NNI, Nearest Neighbor Interpolation; LI, Linear Interpolation; CSI, Cubic Spline Interpolation.