ArticleSleep2026
How many nights are needed? The short-term stability of intraindividual variability in sleep parameters derived from accelerometry data in a cohort of normal sleepers.
Article in Sleep, 2026. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Cited by 4 papers.
What it found
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The abstract states no effect estimate the extractor could read, or names no intervention and outcome on the map, so this paper lights no cell and moves no belief. It is still indexed, cited and linked below.
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Who cites it
4 citing papers in PubMed.
- Orthometria: Metric Fixation in Digital Health and a Framework for Responsible Use in High-Performance Sport.Sports medicine - open · 2026Article
- Article
- Article
- Sleep health differences and night-to-night variability in people with and without HIV in Mwanza, Tanzania: insights from actigraphy and sleep diaries.Sleep advances : a journal of the Sleep Research Society · 2026Article
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Authors and funding
7 authors.
Funding
Abstract
STUDY
objectivesIndividual sleep/wake patterns can be characterized by the intraindividual mean (iM) and variability (iSD), which captures night-to-night fluctuations. Most accelerometry-based sleep studies assess 7-14 nights, which may be insufficient for reliable variability estimates. This pre-registered, large-cohort study quantifies how many nights are needed for reliable sleep iM and iSD estimates using accelerometry.
methodsParticipants (n = 10 412, Mage = 37.75 ± 10.65, 50.00% women) wore a validated wrist-worn biometric device (WHOOP) for one year (3 700 492 person-nights). Total sleep time (TST), sleep onset, midsleep, sleep offset, wake after sleep onset (WASO), and sleep percentage were estimated. Reliability correlation coefficients compared reference values (calculated from all 363 nights) with 2-362 consecutive nights randomly selected per participant, with r > .80 considered reliable. 95% limits of agreement were calculated using the Bland-Altman method.
resultsReliable iM estimates (r > .80) were achieved with 2-7 nights of data, depending on the sleep metric: TST (7 nights), sleep-onset and midsleep (3), sleep-offset and sleep percentage (4), WASO (5). In contrast, reliable iSD estimates required substantially more nights: TST (43 nights), sleep-onset (44), midsleep and sleep-offset (41), sleep percentage (62), and WASO (65). iSDs estimated from 7-14 nights showed poor reliability (r = .50-.67) and wide 95% limits of agreement (e.g. TST: ±50.5 min for 7 nights).
conclusionsFindings highlight the importance of tailoring study periods to the specific sleep metric of interest. Longer monitoring periods may improve diagnostic consistency and inform evidence-based recommendations for sleep assessments in clinical and research settings.
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