Research
Adherence
Social Jet Lag (SJL) measures weekly differences in sleep timing (workdays vs. free days) and is insensitive to day-to-day variability.
Use Social Jet Lag (SJL) only if you want to measure the difference between your workday and weekend sleep schedules. Do not use SJL to assess day-to-day consistency, as it will not detect daily fluctuations in sleep timing or duration.
GoodSupportsHIGH confidence
SJL is a measure of weekly but not daily sleep regularity.
Why this rating
Demonstrated through simulation scenarios where daily variation was introduced while SJL remained constant.
Source
Measuring sleep regularity: theoretical properties and practical usage of existing metrics
Dorothee Fischer et al. · SLEEP · 2021
DOI 10.1093/sleep/zsab103
mechanism_onlyCited 189×
Read the paper DOI resolved against Crossref · corpus check 2026-06-10
More from this paper
- Overall metrics (StDev, IS) overestimate sleep regularity when based on study lengths of 7 days or less, whereas consecutive metrics (SRI, CPD) are more stable but require larger sample sizes.Strong
- The Sleep Regularity Index (SRI) and Interdaily Stability (IS) are sensitive to sleep fragmentation (awakenings) and napping, whereas Standard Deviation (StDev) and Composite Phase Deviation (CPD) are not sensitive to these factors.Good
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