However, there has been an increasing trend in recent years towards utilizing both accelerometer and PPG data for evaluating sleep, which is reflected in the inclusion of 28 such devices in this review, as seen in Fig. 3 .
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However, there has been an increasing trend in recent years towards utilizing both accelerometer and PPG data for evaluating sleep, which is reflected in the inclusion of 28 such devices in this review, as seen in Fig. 3 .