title: Sources of variability in epidemiological studies of sleep using repeated nights of in-home polysomnography: SWAN Sleep Study.
abstract: OBJECTIVE
  To quantify sources of night-to-night variability.
  
  
  METHODS
  This project was conducted in 285 middle-aged African American, Caucasian, and Chinese women from the Study of Women's Health Across the Nation (SWAN) Sleep Study living in Chicago, the Detroit area, Oakland, and Pittsburgh. The study used 3 repeated nights of in-home polysomnography (PSG) measures. Night 1 data included assessment of sleep staging, sleep apnea, and periodic limb movements, while Nights 2 and 3 focused on sleep staging.
  
  
  RESULTS
  Mean total sleep time (TST) increased substantially from 365 minutes on Night 1 to 391 minutes and 380 minutes, respectively, on Nights 2 and 3. Mean percent sleep efficiency (SE%) for the 3 nights were 83%, 85%, and 85%, respectively. Night 1 sleep values were significantly different than Nights 2 and 3 measures except for S2 (%), S1 (min), and Delta (S3+4)%. Nights 2 and 3 differences in variability were negligible. Obesity, past smoking, and financial strain measures were associated with greater Night 1 vs. Night 2 or Night 3 differences. We concluded that there was significant Night 1 vs. Nights 2 and 3 variability and, though relatively modest, it was sufficient to bias estimates of association. Additionally, personal characteristics including smoking, obesity, and financial strain increased night-to-night variability.
  
  
  CONCLUSIONS
  This reports adds new information about between and within person sources of variation with in-home PSG and identifies elements that are essential in the design and planning of future sleep studies of multi-ethnic groups in social and physiological transition states such as the menopause.
authors.affiliation: Department of Epidemiology, University of Michigan School of Public Health, Ann Arbor, MI 48109, USA. zhenghy@umich.edu
authors.forename: Huiyong
authors.initials: H
authors.lastname: Zheng
authors.forename: MaryFran
authors.initials: M
authors.lastname: Sowers
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Buysse
authors.forename: Flavia
authors.initials: F
authors.lastname: Consens
authors.forename: Howard M
authors.initials: HM
authors.lastname: Kravitz
authors.forename: Karen A
authors.initials: KA
authors.lastname: Matthews
authors.forename: Jane F
authors.initials: JF
authors.lastname: Owens
authors.forename: Ellen B
authors.initials: EB
authors.lastname: Gold
authors.forename: Martica
authors.initials: M
authors.lastname: Hall
mesh_terms: D003430:Cross-Sectional Studies; D005260:Female; D006699:Home Care Services; D006801:Humans; D008875:Middle Aged; D017286:Polysomnography / Q000379:methods*; D012890:Sleep / Q000502:physiology*; D012891:Sleep Apnea Syndromes / Q000175:diagnosis / Q000503:physiopathology; D012894:Sleep Stages / Q000502:physiology; D013997:Time Factors