How is it most constructive to interpret data from a wrist-worn device when compared to PSG?

As an excellent sleep duration and efficiency meter.

When comparing consumer wearable data to the high standard set by PSG, the data should be interpreted pragmatically based on what the sensors are capable of measuring effectively. Because wearables primarily use motion (actigraphy) and heart rate, they excel at quantifying the overall time spent asleep (Total Sleep Time) and how often the user was restless or awake during the night (efficiency/fragmentation). However, they inherently struggle to validate the subtle neurological stages like deep sleep, often underestimating it compared to EEG findings. Therefore, viewing the wearable as a robust tool for measuring duration and efficiency, rather than a comprehensive clinical replacement, yields the most actionable insights.