title: The relationships between sex, age, geography and time in bed in adolescents: a meta-analysis of data from 23 countries.
abstract: OBJECTIVE
  To quantify the relationships between age, sex and country of residence and sleep time (time in bed) in young people aged 9-18 years.
  
  
  METHODS
  Thirty studies of sleep patterns in healthy adolescents from the last 30 years in 20 countries were reviewed. Monte Carlo simulation generated pseudo-data where only summary statistics were available. Raw and pseudo-data were combined, generating a total of 92,977 data points. A mixed model, clustering on countries, analysed data for school and non-school days separately.
  
  
  RESULTS
  Sleep time varied with sex, age and geographical region. School day sleep differed slightly between boys and girls, girls sleeping 11 min/night more than boys (p = 0.003). On non-school days, girls slept 29 min more each day (p = 0.003). Sleep time declined with age, - 14 min/day per year of age (school days), and seven min/night per year of age (non-school days). Large differences between countries, showed adolescents from Asian countries sleeping 40-60 min less each night than Americans, and 60-120 min less than Europeans.
  
  
  CONCLUSIONS
  Sex, age, geographical region and day type interact and predict sleep patterns in adolescents. One consistent trend is the increasing gap between sleep on school days and non-school days as adolescents get older.
authors.affiliation: Sansom Institute, Division of Health Sciences, University of South Australia, Australia.
authors.forename: Tim
authors.initials: T
authors.lastname: Olds
authors.forename: Sarah
authors.initials: S
authors.lastname: Blunden
authors.forename: John
authors.initials: J
authors.lastname: Petkov
authors.forename: Fabricio
authors.initials: F
authors.lastname: Forchino
mesh_terms: D000203:Activities of Daily Living; D000293:Adolescent; D000294:Adolescent Behavior; D001208:Asia / Q000453:epidemiology; D001294:Attitude to Health; D002648:Child; D002652:Child Behavior; D016000:Cluster Analysis; D005060:Europe / Q000453:epidemiology; D005260:Female; D015438:Health Behavior; D006801:Humans; D008019:Life Style; D008297:Male; D009656:North America / Q000453:epidemiology; D011788:Quality of Life; D012890:Sleep; D012892:Sleep Deprivation / Q000453:epidemiology; D012893:Sleep Wake Disorders / Q000453:epidemiology*; D012931:Social Environment; D012959:Socioeconomic Factors; D014851:Wakefulness