Response To: Investigating sources of inaccuracy in wearable optical heart rate sensors

Recently, Bent and colleagues (2020) published a timely and well-written paper examining the role of skin tone on inaccurate readings in consumer and medical grade wearables (Empatica E4 + ; Apple Watch 4; Fitbit Charge 2; Garmin Vivosmart 3; Xiaomi Miband; Biovotion Everion) 1 . They found no significant difference in accuracy across skin tones, but did find differences by devices in response to changes in activity. This finding is in contrast to previously reported studies finding wearables using green light technology had larger errors rates in tracking heart rate and energy expenditure for individuals with darker skin tones 2 , especially if exercising 3 . So while Bent and colleagues’ paper is a model in reporting in many ways, due to the incredibly important nature of this topic, it is crucial to appraise their paper to advance scientific discourse and highlight several recommendations for future researchers. Specifically, I believe their findings may be misleading due to their small sample size, which may miss important interaction effects of confounding variables and skin tone, and their use of the Fitzpatrick Skin Type Scale, which has a substantial literature of racial biases 4 , 5 , 6 , weak correlation with skin color, and large within-group variations of skin tone 4 , 7 , 8 . As such, I am concerned their findings on skin tone are not accurate and will be used to limit or misrepresent future research on inaccuracies of skin tone in wearable devices.