title: Correlates of sedentary time in children: a multilevel modelling approach.
abstract: BACKGROUND
  Sedentary behaviour (SB) has been implicated as a potential risk factor for chronic disease. Since children spend most of their awake time in schools, this study aimed to identify individual- and school-level correlates of sedentary time using a multilevel approach, and to determine if these correlates have a similar effect in normal weight (NW) and overweight/obese (O/O) children.
  
  
  METHODS
  Sample comprised 686 Portuguese children aged 9-10 years from 23 schools that took part in the ISCOLE project. Actigraph GT3X + accelerometers were used 24 hours/day for 7 days to assess sedentary time (daily minutes <100 counts/min); BMI was computed and WHO cut-points were used to classify subjects as NW or O/O. Sex, BMI, number of siblings, family income, computer use on school days, and sleep time on school days were used as individual-level correlates. At the school level, school size (number of students), percentage of students involved in sports or physical activity (PA) clubs, school promotion of active transportation, and students' access to equipment outside school hours were used. All multilevel modelling analysis was done in SPSS, WINPEPI, and HLM.
  
  
  RESULTS
  School-level correlates explain ≈ 6.0% of the total variance in sedentary time. Results (β ± SE) showed that boys (-30.85 ± 5.23), children with more siblings (-8.56 ± 2.71) and those who sleep more (-17.78 ± 3.06) were less sedentary, while children with higher family income were more sedentary (4.32 ± 1.68). At the school level, no variable was significantly correlated with sedentary time. Among weight groups, variables related to sedentary time in NW were sex, sleep time and family income, while in O/O sex, number of siblings and sleep time were significant correlates. No school-level predictors were significantly associated in either of the weight groups.
  
  
  CONCLUSIONS
  Notwithstanding the relevance of the school environment in the reduction of children's sedentary time, individual and family characteristics played a more relevant role than the school context in this study.
authors.forename: Thayse Natacha
authors.initials: TN
authors.lastname: Gomes
authors.forename: Fernanda Karina
authors.initials: FK
authors.lastname: dos Santos
authors.forename: Daniel
authors.initials: D
authors.lastname: Santos
authors.forename: Sara
authors.initials: S
authors.lastname: Pereira
authors.forename: Raquel
authors.initials: R
authors.lastname: Chaves
authors.forename: Peter Todd
authors.initials: PT
authors.lastname: Katzmarzyk
authors.affiliation: CIFI2D, Faculty of Sport, University of Porto, Rua Dr Plácido Costa, 91, Porto 4200-450, Portugal. jmaia@fade.up.pt.
authors.forename: José
authors.initials: J
authors.lastname: Maia
mesh_terms: D015992:Body Mass Index; D001835:Body Weight; D002648:Child; D015444:Exercise; D005191:Family Characteristics; D005260:Female; D006801:Humans; D007182:Income; D008297:Male; D008954:Models, Biological; D009043:Motor Activity; D055361:Multilevel Analysis; D009765:Obesity / Q000209:etiology*; D050177:Overweight; D012016:Reference Values; D012574:Schools; D057185:Sedentary Behavior; D012737:Sex Factors; D012890:Sleep