Plain-language definitions grounded in the clinical and regulatory literature.
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Metric
What it isThe percentage of time in bed actually spent asleep — total sleep time divided by total time in bed, multiplied by 100. Normal sleep efficiency in healthy adults is ≥85%.
Why it mattersSleep efficiency captures sleep quality independent of duration. Someone spending 9 hours in bed while sleeping only 6 hours (67% efficiency) has disrupted sleep regardless of time opportunity. It is a primary outcome measure in insomnia treatment and the criterion that drives CBT-I’s sleep restriction titration.
Think of it like thisSleep efficiency is like a productivity ratio for your bed. If you spend 9 hours in bed but only sleep 7, you’re running at 78% — not bad, but your organization has a process problem.
Sleep efficiency (SE) = (Total Sleep Time / Total Time in Bed) × 100. Clinically, SE ≥85% is considered normal in adults. SE <85% consistently is consistent with insomnia disorder and is a primary outcome measure in CBT-I trials. Measured by PSG (most accurate), actigraphy (overestimates by ~5%), or sleep diary (overestimates by ~7%).
MechanismLow sleep efficiency reflects fragmentation of sleep architecture through elevated sleep onset latency (anxiety-driven hyperarousal), multiple nighttime awakenings (wake after sleep onset — from sleep apnea, pain, or nocturia), or early morning awakening (common in depression and advanced circadian phase). Each pattern has distinct pathophysiology and clinical management implications.
Scientific ConsensusThe 85% threshold is well-established in clinical practice guidelines for insomnia. SE is a primary outcome measure in CBT-I trials. Sleep restriction therapy titrates time in bed based on SE — when SE exceeds 85-90% for 5+ consecutive days, the window is extended. SE measured by PSG, actigraphy, and diary yield systematically different absolute values but track change consistently.
Active DebateOptimal SE threshold for older adults who naturally have lower SE. Whether actigraphy and PSG SE are clinically interchangeable. How much intraindividual night-to-night variability is normal vs. pathological.
Emerging ResearchWhether night-to-night SE variability is more clinically informative than average SE. Wearable-measured SE as a population-level health indicator. Whether SE thresholds should differ for older adults.
Key ResearchThe 85% threshold derives from CBT-I outcome literature. Marino et al. (2013) validated actigraphy SE vs. PSG. Morin et al. (1994) used SE as the primary CBT-I outcome metric.
— Validation study of actigraphy-measured SE vs. PSG gold standard across 77 adults
— Established SE as primary CBT-I outcome measure and defined 85% threshold in treatment context
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