{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,13]],"date-time":"2026-10-13T23:01:09Z","timestamp":1791932469417,"version":"4.3.4"},"reference-count":42,"publisher":"Oxford University Press (OUP)","issue":"6","license":[{"start":{"date-parts":[[2026,2,28]],"date-time":"2026-02-28T00:00:00Z","timestamp":1772236800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by-nc\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100000923","name":"Australian Research Council","doi-asserted-by":"publisher","award":["IE240100162"],"award-info":[{"award-number":["IE240100162"]}],"id":[{"id":"10.13039\/501100000923","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/100000049","name":"National Institute on Aging","doi-asserted-by":"publisher","award":["T32 AG049676"],"award-info":[{"award-number":["T32 AG049676"]}],"id":[{"id":"10.13039\/100000049","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/100008321","name":"The Pennsylvania State University","doi-asserted-by":"publisher","id":[{"id":"10.13039\/100008321","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"published-print":{"date-parts":[[2026,6,15]]},"abstract":"<jats:title>Abstract<\/jats:title>\n                  <jats:sec>\n                    <jats:title>Study Objectives<\/jats:title>\n                    <jats:p>Individual 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\u201314 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.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Methods<\/jats:title>\n                    <jats:p>Participants (n\u00a0=\u200910\u2009412, Mage\u00a0=\u200937.75\u00a0\u00b1\u00a010.65, 50.00% women) wore a validated wrist-worn biometric device (WHOOP) for one year (3\u2009700\u2009492 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\u2013362 consecutive nights randomly selected per participant, with r\u2009&amp;gt;\u2009.80 considered reliable. 95% limits of agreement were calculated using the Bland\u2013Altman method.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>Reliable iM estimates (r\u2009&amp;gt;\u2009.80) were achieved with 2\u20137 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\u201314 nights showed poor reliability (r\u2009=\u2009.50\u2013.67) and wide 95% limits of agreement (e.g. TST: \u00b150.5\u00a0min for 7 nights).<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusions<\/jats:title>\n                    <jats:p>Findings 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.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.1093\/sleep\/zsag040","type":"journal-article","created":{"date-parts":[[2026,2,28]],"date-time":"2026-02-28T08:55:08Z","timestamp":1772268908000},"source":"Crossref","is-referenced-by-count":16,"title":["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"],"prefix":"10.1093","volume":"49","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-7714-4630","authenticated-orcid":false,"given":"Josh","family":"Leota","sequence":"first","affiliation":[{"name":"School of Psychological Sciences, Monash University , Melbourne, Vic ,","place":["Australia"]},{"name":"Division of Sleep and Circadian Disorders, Department of Medicine, Brigham and Women\u2019s Hospital , Boston, MA ,","place":["United States"]},{"name":"Department of Research, Algorithms, and Data Science, Whoop Inc. , Boston, MA ,","place":["United States"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1835-7134","authenticated-orcid":false,"given":"Brett A","family":"Messman","sequence":"additional","affiliation":[{"name":"Department of Psychology, University of North Texas , Denton, TX ,","place":["United States"]},{"name":"Center for Healthy Aging, The Pennsylvania State University, State College , PA ,","place":["United States"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0089-8167","authenticated-orcid":false,"given":"Flora","family":"Le","sequence":"additional","affiliation":[{"name":"School of Psychological Sciences, Monash University , Melbourne, Vic ,","place":["Australia"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0000-6712-6570","authenticated-orcid":false,"given":"Summer","family":"Jasinski","sequence":"additional","affiliation":[{"name":"Department of Research, Algorithms, and Data Science, Whoop Inc. , Boston, MA ,","place":["United States"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4203-5693","authenticated-orcid":false,"given":"Emily R","family":"Capodilupo","sequence":"additional","affiliation":[{"name":"Department of Research, Algorithms, and Data Science, Whoop Inc. , Boston, MA ,","place":["United States"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4549-9266","authenticated-orcid":false,"given":"Elise R","family":"Facer-Childs","sequence":"additional","affiliation":[{"name":"School of Psychological Sciences, Monash University , Melbourne, Vic ,","place":["Australia"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0271-6702","authenticated-orcid":false,"given":"Joshua F","family":"Wiley","sequence":"additional","affiliation":[{"name":"School of Psychological Sciences, Monash University , Melbourne, Vic ,","place":["Australia"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"286","published-online":{"date-parts":[[2026,2,28]]},"reference":[{"issue":"6","key":"2026061512445128100_ref1","doi-asserted-by":"publisher","first-page":"801","DOI":"10.1016\/j.sleh.2023.07.016","article-title":"The importance of sleep regularity: a consensus statement of the National Sleep Foundation sleep timing and variability panel","volume":"9","author":"Sletten","year":"2023","journal-title":"Sleep Health"},{"key":"2026061512445128100_ref2","doi-asserted-by":"publisher","first-page":"108","DOI":"10.1016\/j.smrv.2015.06.003","article-title":"Beyond the mean: a systematic review on the correlates of daily intraindividual variability of sleep\/wake patterns","volume":"28","author":"Bei","year":"2016","journal-title":"Sleep Med Rev"},{"issue":"10","key":"2026061512445128100_ref3","doi-asserted-by":"publisher","first-page":"S232","DOI":"10.1139\/apnm-2020-0032","article-title":"Sleep timing, sleep consistency, and health in adults: a systematic review","volume":"45","author":"Chaput","year":"2020","journal-title":"Appl Physiol Nutr Metab"},{"key":"2026061512445128100_ref4","doi-asserted-by":"publisher","first-page":"585","DOI":"10.2147\/NSS.S452033","article-title":"The emerging importance of sleep regularity on cardiovascular health and cognitive impairment in older adults: a review of the literature","volume":"16","author":"Qin","year":"2024","journal-title":"Nat Sci Sleep"},{"issue":"2","key":"2026061512445128100_ref5","doi-asserted-by":"crossref","first-page":"233","DOI":"10.1111\/1469-8986.3620233","article-title":"How many nights are enough? 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