title: Autism and intellectual disability are differentially related to sociodemographic background at birth.
abstract: BACKGROUND
  Research findings investigating the sociodemographics of autism spectrum disorder (ASD) have been inconsistent and rarely considered the presence of intellectual disability (ID).
  
  
  METHODS
  We used population data on Western Australian singletons born from 1984 to 1999 (n = 398,353) to examine the sociodemographic characteristics of children diagnosed with ASD with or without ID, or ID without ASD compared with non-affected children.
  
  
  RESULTS
  The profiles for the four categories examined, mild-moderate ID, severe ID, ASD without ID and ASD with ID varied considerably and we often identified a gradient effect where the risk factors for mild-moderate ID and ASD without ID were at opposite extremes while those for ASD with ID were intermediary. This was demonstrated clearly with increased odds of ASD without ID amongst older mothers aged 35 years and over (odds ratio (OR) = 1.69 [CI: 1.18, 2.43]), first born infants (OR = 2.78; [CI: 1.67, 4.54]), male infants (OR = 6.57 [CI: 4.87, 8.87]) and increasing socioeconomic advantage. In contrast, mild-moderate ID was associated with younger mothers aged less than 20 years (OR = 1.88 [CI: 1.57, 2.25]), paternal age greater than 40 years (OR = 1.59 [CI: 1.36, 1.86]), Australian-born and Aboriginal mothers (OR = 1.60 [CI: 1.41, 1.82]), increasing birth order and increasing social disadvantage (OR = 2.56 [CI: 2.27, 2.97]). Mothers of infants residing in regional or remote areas had consistently lower risk of ASD or ID and may be linked to reduced access to services or under-ascertainment rather than a protective effect of location.
  
  
  CONCLUSIONS
  The different risk profiles observed between groups may be related to aetiological differences or ascertainment factors or both. Untangling these pathways is challenging but an urgent public health priority in view of the supposed autism epidemic.
authors.affiliation: Telethon Institute for Child Health Research, Centre for Child Health Research, The University of Western Australia, West Perth, Western Australia, Australia.
authors.forename: Helen
authors.initials: H
authors.lastname: Leonard
authors.forename: Emma
authors.initials: E
authors.lastname: Glasson
authors.forename: Natasha
authors.initials: N
authors.lastname: Nassar
authors.forename: Andrew
authors.initials: A
authors.lastname: Whitehouse
authors.forename: Ami
authors.initials: A
authors.lastname: Bebbington
authors.forename: Jenny
authors.initials: J
authors.lastname: Bourke
authors.forename: Peter
authors.initials: P
authors.lastname: Jacoby
authors.forename: Glenys
authors.initials: G
authors.lastname: Dixon
authors.forename: Eva
authors.initials: E
authors.lastname: Malacova
authors.forename: Carol
authors.initials: C
authors.lastname: Bower
authors.forename: Fiona
authors.initials: F
authors.lastname: Stanley
mesh_terms: D000328:Adult; D001321:Autistic Disorder / Q000150:complications* / Q000453:epidemiology*; D003710:Demography; D005260:Female; D006801:Humans; D008607:Intellectual Disability / Q000150:complications* / Q000453:epidemiology*; D008297:Male; D008423:Maternal Age; D015999:Multivariate Analysis; D036801:Parturition; D015995:Prevalence; D012959:Socioeconomic Factors; D014904:Western Australia / Q000453:epidemiology; D055815:Young Adult