Fig. 4: Accuracy of passive HR and RHR measurements by PHRM in free-living conditions.

a, Bland–Altman plot showing the agreement between PHRM-estimated HR values and reference ECG measurements. Colours indicate the confidence level of PHRM predictions. Dashed lines show the bias, lower and upper limits of agreement adjusted for repeated measurements with unequal numbers of replicates. b, Box plots showing the distribution of MAPE values for individual participants, grouped by skin pigmentation. n = 39, 29 and 39 participants in skin-tone groups 1, 2 and 3, respectively. The box bounds the IQR divided by the median, and whiskers extend to a maximum of 1.5 × IQR beyond the box. Red dashed line indicates the prespecified accuracy target of MAPE <10%. c, Bland–Altman plot showing the agreement between PHRM-estimated daily RHR values and the reference wearable HR tracker measurements. Colours indicate the day number since the start of RHR predictions. Dashed lines show the bias, lower and upper limits of agreement adjusted for repeated measurements with unequal numbers of replicates. d, MAE of PHRM-estimated RHR as a function of day number since the start of RHR predictions, grouped by skin pigmentation. Shaded areas indicate 95% CIs. Red dashed line indicates the prespecified accuracy target of MAE <5 bpm.