title: Changes in diagnosis rates and behavioural traits of autism spectrum disorder over time.
abstract: BACKGROUND
  The increased proportion of UK children diagnosed with autism spectrum disorder (ASD) has been attributed to improved identification, rather than true increase in incidence.
  
  
  OBJECTIVE
  To explore whether the proportion of children with diagnosis of ASD and/or the proportion with associated behavioural traits had increased over a 10-year period.
  
  
  METHODS
  A cross-cohort comparison using regression to compare prevalence of diagnosis and behavioural traits over time. Participants were children aged 7 years assessed in 1998/1999 (n=8139) and 2007/2008 (n=13 831).
  
  
  RESULTS
  During 1998/1999, 1.09% (95% CI 0.86-1.37) of children were reported as having ASD diagnosis compared with 1.68% (95% CI 1.42-2.00) in 2007/2008: risk ratio (RR)=1.55 (95% CI 1.17-2.06),P=0.003. The proportion of children in the population with behavioural traits associated with ASD was also larger in the later cohort: RR=1.61 (95% CI 1.35-1.92),P<0.001. Increased odds of diagnosis at the later time point was partially accounted for by adjusting for the increased proportion of children with ASD-type traits.
  
  
  CONCLUSIONS
  Increased ASD diagnosis may partially reflect increase in rates of behaviour associated with ASD and/or greater parent/teacher recognition of associated behaviours.
  
  
  BACKGROUND
  None.
  © The Royal College of Psychiatrists 2015. This is an open access article distributed under the terms of the Creative Commons Non-Commercial, No Derivatives (CC BY-NC-ND) licence.
authors.affiliation: , PhD, Institute of Health Research, University of Exeter Medical School, Exeter, UK.
authors.forename: Ginny
authors.initials: G
authors.lastname: Russell
authors.affiliation: , PhD, Institute of Psychological Medicine and Clinical Neurosciences, Cardiff University School of Medicine, Cardiff, UK.
authors.forename: Stephan
authors.initials: S
authors.lastname: Collishaw
authors.affiliation: , Centre for Child & Adolescent Health, School of Social & Community Medicine, University of Bristol, Bristol, UK.
authors.forename: Jean
authors.initials: J
authors.lastname: Golding
authors.affiliation: , Department of Sociology, Philosophy and Anthropology, School of Social Science, University of Exeter, Exeter, UK.
authors.forename: Susan E
authors.initials: SE
authors.lastname: Kelly
authors.affiliation: , Institute of Health Research, University of Exeter Medical School, Exeter, UK.
authors.forename: Tamsin
authors.initials: T
authors.lastname: Ford