Sleep consistency
Seems to be as important or more important than the amount of sleep. Holmes talks about incredible HRV improvements while focusing on this.
Some resources
- Whoop blog definition and advocation.
- Holmes' paper
- Study showing real impact on academic performance
Not sure on the math to actually calculate this? Holmes' paper indicates that it's proprietary:
Sleep Consistency (a proprietary metric of the WHOOP platform adapated from the Sleep Regularity Index)
while citing the Philips paper, which defines as
Motivated by our interest in capturing changes in sleep timing on a day-to-day (circadian) timescale, we con- structed a novel metric for sleep regularity, called the Sleep Regularity Index (SRI). This index calculates the per- centage probability of an individual being in the same state (asleep vs. awake) at any two time-points 24 h apart, averaged across the study. The index is scaled so that an individual who sleeps and wakes at exactly the same times each day scores 100, whereas an individual who sleeps and wakes at random scores 0. This index is constructed on the reasoning that changes in sleep schedules from one 24-h interval to the next may cause circadian disruption and thus impact normal biological functioning and health. The SRI differs from previous approaches in that it does not require designation of a main daily sleep episode, and can thus be applied in populations such as college students, where additional daytime sleep episodes and all-nighters are commonly observed.
Very exhaustive review of different metrics including SRI from Fischer.