title: Improving actigraphic sleep estimates in insomnia and dementia: how many nights?
abstract: In order to investigate how the duration of actigraphic recordings affects the reliability of actigraphic estimates of sleep and 24-h activity rhythm variables, two to 3 weeks of actigraphy were recorded, from which pairs of variables derived from two periods of increasing length (1-10 days) were compared. Two groups were studied: (1) 10 subjects suffering from primary insomnia; and (2) 12 demented elderly subjects living semi-independently in group care facilities of homes for the elderly. Actigraphic estimates of primary measures of sleep (duration and efficiency) and of the 24-h activity pattern (interdaily stability, intradaily variability and amplitude) were calculated on variable lengths of the actigraphic recordings. The average absolute difference of two estimates decreased - and reliability increased - strongly with an increasing number of days analysed. An acceptable reliability of the interdaily stability estimate required more than 7 days of recording. It can be concluded that a valuable improvement in the reliability of actigraphic sleep estimates can be obtained by simply increasing the number of recording nights. The results support the importance of day-to-day variability in insomnia and dementia that has already been previously noted by others, and even suggest the presence of 'week-to-week' variability. This variability may have been involved in the equivocal results of treatment studies in insomnia and dementia where outcome measures were based on a limited number of nights. Such studies could profit from extension of the recording duration to, e.g. 2 weeks, and from the inclusion of variability measures as measures of clinical interest.
authors: Netherlands Institute for Neuroscience, an Institute of the Royal Netherlands Academy of Arts and Sciences, Amsterdam, The Netherlands. e.van.someren@nin.knaw.nl
authors: Eus J W
authors: EJ
authors: VAN Someren
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D002940:Circadian Rhythm; D003704:Dementia / Q000150:complications*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic / Q000295:instrumentation*; D017286:Polysomnography / Q000379:methods; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D020178:Sleep Disorders, Circadian Rhythm / Q000175:diagnosis* / Q000209:etiology; D007319:Sleep Initiation and Maintenance Disorders / Q000175:diagnosis* / Q000209:etiology; D011795:Surveys and Questionnaires