title: Cohort effects explain the increase in autism diagnosis among children born from 1992 to 2003 in California.
abstract: BACKGROUND
  The incidence and prevalence of autism have dramatically increased over the last 20 years. Decomposition of autism incidence rates into age, period and cohort effects disentangle underlying domains of causal factors linked to time trends. We estimate an age-period-cohort effect model for autism diagnostic incidence overall and by level of functioning.
  
  
  METHODS
  Data are drawn from sequential cohorts of all 6 501 262 individuals born in California from 1992 to 2003. Autism diagnoses from 1994 to 2005 were ascertained from the California Department of Development Services Client Development and Evaluation Report.
  
  
  RESULTS
  Compared with those born in 1992, each successively younger cohort has significantly higher odds of an autism diagnosis than the previous cohort, controlling for age and period effects. For example, individuals born in 2003 have 16.6 times the odds of an autism diagnosis compared with those born in 1992 [95% confidence interval (CI) 7.8-35.3]. The cohort effect observed in these data is stronger for high than for low-functioning children with an autism diagnosis.
  
  
  CONCLUSIONS
  Autism incidence in California exhibits a robust and linear positive cohort effect that is stronger among high-functioning children with an autism diagnosis. This finding indicates that the primary drivers of the increases in autism diagnoses must be factors that: (i) have increased linearly year-to-year; (ii) aggregate in birth cohorts; and (iii) are stronger among children with higher levels of functioning.
authors.affiliation: Department of Epidemiology, Columbia University, New York, NY, USA.
authors.forename: Katherine M
authors.initials: KM
authors.lastname: Keyes
authors.forename: Ezra
authors.initials: E
authors.lastname: Susser
authors.forename: Keely
authors.initials: K
authors.lastname: Cheslack-Postava
authors.forename: Christine
authors.initials: C
authors.lastname: Fountain
authors.forename: Kayuet
authors.initials: K
authors.lastname: Liu
authors.forename: Peter S
authors.initials: PS
authors.lastname: Bearman
mesh_terms: D000367:Age Factors; D001321:Autistic Disorder / Q000453:epidemiology*; D002140:California / Q000453:epidemiology; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D006801:Humans; D015994:Incidence; D007223:Infant; D008297:Male; D015233:Models, Statistical; D015995:Prevalence; D012307:Risk Factors