Bland–Altman plot of agreement between couple of tested variables measuring autonomic nervous system modulation, corrected for within-subject variance with a linear mixed model. Thick lines represent the bias, and dotted lines represent ±1.96 SD. (A) αHF versus PPGA, bias = −0.04 (95% CI, −44.3 to 44.2); (B) αHF versus ANSS, bias = 0.09 (95% CI, −34.8 to 34.9); (C) αHF versus ANSSi, bias = 0.23 (95% CI, −22.7 to 23.2); (D) LF/HF versus ANSSi, bias = 0.96 (95% CI, −8.7 to 10.8). All data are given in normalized units. ANSS = autonomic nervous system state; ANSSi = autonomic nervous system state index; LF/HF = sympathovagal balance; PPGA = pulse photo-plethysmographic amplitude; αHF = baroreflex sensitivity in high-frequency band.