“…25 According to Ciccone et al and Antali et al, most metrics are omitted due to redundancy or due to evidence of them being prone to artifacts, or artificial noise, leaving SDNN, SD1, and SD2 as metrics for evaluation. 26,27 In a recent publication, Natarajan et al presented normative values for PPG sensor-based HRV features of more than 8 million Fitbit® users. 28 We divided the computed metrics by the provided age, sex, and time-of-day specific normative values, obtaining percentage scores.. 28,29 These represent the percentage deviation of the measured value from the reference, mitigating the influence of age, sex, and time-of-day differences in group comparisons (also see Figure S2).…”