Efficiency was defined as total sleep time (TST) over time in bed (lights off to lights on for PSG, and recording time for home tests). Wake after sleep ons...

https://www.apple.com/jp/healthcare/docs/site/Estimating_Sleep_Stages_from_Apple_Watch_Sept_2023.pdf

or vice versa (REF_HTF) to control for the variable of listening fatigue or practice effects after。

https://www.apple.com/jp/health/pdf/Hearing_Health_Features_on_AirPods_Pro_2_October_2024.pdf