title: Age at first autism spectrum disorder diagnosis: the role of birth cohort, demographic factors, and clinical features.
abstract: OBJECTIVE
  This study sought to identify factors that may be associated with delays in autism spectrum disorder (ASD) diagnosis, including birth cohort, sociodemographic characteristics, and clinical features.
  
  
  METHODS
  Participants included 1716 children and adolescents with ASD enrolled in the Autism Speaks Autism Treatment Network (AS-ATN) between the years 2008 and 2011. Data were collected at enrollment using AS-ATN parent- and clinician-report forms and standardized measures of I.Q., ASD symptoms, adaptive function, and psychiatric symptoms.
  
  
  RESULTS
  Age at first ASD diagnosis was positively correlated with current age, suggesting a birth cohort effect. Sociodemographic and clinical features were also associated with age at diagnosis, even after controlling for current age. Hierarchical linear regression results showed that older current age, lower socioeconomic status (SES), higher I.Q. score, and lower levels of autism symptoms were associated with later age at initial diagnosis. There was also a significant interaction between current age and I.Q., with higher functioning children being diagnosed at younger ages than in previous years.
  
  
  CONCLUSIONS
  Early diagnosis of ASD is critically important for improving access to interventions; however, many children experience diagnostic delays. In this sample, children from the most recent birth cohorts were diagnosed earlier, suggesting that early signs of ASD are being increasingly recognized. However, socioeconomic barriers to diagnosis still seem to exist. Children with less severe ASD symptoms and with higher I.Q. are also diagnosed at later ages. Efforts are still needed to reduce diagnostic disparities for families of low SES and to improve early recognition of more subtle symptoms.
authors.affiliation: *Department of Health Psychology and Thompson Center for Autism and Neurodevelopmental Disorders, University of Missouri, Columbia, MO; †Department of Psychiatry, University of Pittsburgh School of Medicine, Pittsburgh, PA; ‡Department of Psychiatry and Behavioral Sciences, Johns Hopkins University School of Medicine and Center for Autism and Related Disorders, Kennedy Krieger Institute, Baltimore, MD; §Lurie Center for Autism, MassGeneral Hospital for Children, and Harvard Medical School, Boston, MA; ‖Departments of Pediatrics and Psychology, Nationwide Children's Hospital, Ohio State University, Columbus, OH.
authors.forename: Micah O
authors.initials: MO
authors.lastname: Mazurek
authors.forename: Benjamin L
authors.initials: BL
authors.lastname: Handen
authors.forename: Ericka L
authors.initials: EL
authors.lastname: Wodka
authors.forename: Lisa
authors.initials: L
authors.lastname: Nowinski
authors.forename: Eric
authors.initials: E
authors.lastname: Butter
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Engelhardt
mesh_terms: D000293:Adolescent; D000367:Age Factors; D000067877:Autism Spectrum Disorder / Q000175:diagnosis*; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007360:Intelligence / Q000502:physiology*; D008297:Male; D012720:Severity of Illness Index; D012923:Social Class; D013997:Time Factors