title: Trend analyses in the health behaviour in school-aged children study: methodological considerations and recommendations.
abstract: BACKGROUND
  This article presents the scope and development of the Health Behaviour in School-aged Children (HBSC) study, reviews trend papers published on international HBSC data up to 2012 and discusses the efforts made to produce reliable trend analyses.
  
  
  METHODS
  The major goal of this article is to present the statistical procedures and analytical strategies for upholding high data quality, as well as reflections from the authors of this article on how to produce reliable trends based on an international study of the magnitude of the HBSC study. HBSC is an international cross-sectional study collecting data from adolescents aged 11-15 years, on a broad variety of health determinants and health behaviours.
  
  
  RESULTS
  A number of methodological challenges have stemmed from the growth of the HBSC-study, in particular given that the study has a focus on monitoring trends. Some of those challenges are considered. When analysing trends, researchers must be able to assess whether a change in prevalence is an expression of an actual change in the observed outcome, whether it is a result of methodological artefacts, or whether it is due to changes in the conceptualization of the outcome by the respondents.
  
  
  CONCLUSIONS
  The article present recommendations to take a number of the considerations into account. The considerations imply methodological challenges, which are core issues in undertaking trend analyses.
authors: 1 Section of Social Medicine, University of Copenhagen, Copenhagen, Denmark cwsc@sund.ku.dk.
authors: Christina W
authors: CW
authors: Schnohr
authors: 2 School of Health Sciences, NUI Galway, Galway, Ireland.
authors: Michal
authors: M
authors: Molcho
authors: 3 National Institute of Public Health, University of Southern Denmark, Copenhagen, Denmark.
authors: Mette
authors: M
authors: Rasmussen
authors: 4 Department of Psychosocial Science, Faculty of Psychology, University of Bergen, Bergen, Norway.
authors: Oddrun
authors: O
authors: Samdal
authors: 5 Department of Interdisciplinary Social Sciences, Utrecht University, Utrecht, The Netherlands.
authors: Margreet
authors: M
authors: de Looze
authors: 6 NSH Greater Glasgow & Clyde, Public Health Directorate, Glasgow, UK.
authors: Kate
authors: K
authors: Levin
authors: 7 Knowledge and Analytical Services, Welsh Government, Cardiff, UK.
authors: Chris J
authors: CJ
authors: Roberts
authors: 8 INSERM UMR, Université Toulouse, Toulouse, France.
authors: Virginie
authors: V
authors: Ehlinger
authors: 3 National Institute of Public Health, University of Southern Denmark, Copenhagen, Denmark.
authors: Rikke
authors: R
authors: Krølner
authors: 9 Department of Public Health and Paediatrics, University of Turin, Turin, Italy.
authors: Paola
authors: P
authors: Dalmasso
authors: 4 Department of Psychosocial Science, Faculty of Psychology, University of Bergen, Bergen, Norway.
authors: Torbjørn
authors: T
authors: Torsheim
mesh_terms: D000293:Adolescent; D000294:Adolescent Behavior; D000067697:Adolescent Health / Q000639:trends*; D002648:Child; D005060:Europe; D005260:Female; D006304:Health Status; D006306:Health Surveys; D006801:Humans; D008297:Male; D009656:North America; D012107:Research Design