title: Prevalence of autism in a US metropolitan area.
abstract: BACKGROUND
  Concern has been raised about possible increases in the prevalence of autism. However, few population-based studies have been conducted in the United States.
  
  
  OBJECTIVE
  To determine the prevalence of autism among children in a major US metropolitan area and to describe characteristics of the study population.
  
  
  METHODS
  Study of the prevalence of autism among children aged 3 to 10 years in the 5 counties of metropolitan Atlanta, Ga, in 1996. Cases were identified through screening and abstracting records at multiple medical and educational sources, with case status determined by expert review.
  
  
  METHODS
  Autism prevalence by demographic factors, levels of cognitive functioning, previous autism diagnoses, special education eligibility categories, and sources of identification.
  
  
  RESULTS
  A total of 987 children displayed behaviors consistent with Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition criteria for autistic disorder, pervasive developmental disorder-not otherwise specified, or Asperger disorder. The prevalence for autism was 3.4 per 1000 (95% confidence interval [CI], 3.2-3.6) (male-female ratio, 4:1). Overall, the prevalence was comparable for black and white children (black, 3.4 per 1000 [95% CI, 3.0-3.7] and white, 3.4 per 1000 [95% CI, 3.2-3.7]). Sixty-eight percent of children with IQ or developmental test results (N = 880) had cognitive impairment. As severity of cognitive impairment increased from mild to profound, the male-female ratio decreased from 4.4 to 1.3. Forty percent of children with autism were identified only at educational sources. Schools were the most important source for information on black children, children of younger mothers, and children of mothers with less than 12 years of education.
  
  
  CONCLUSIONS
  The rate of autism found in this study was higher than the rates from studies conducted in the United States during the 1980s and early 1990s, but it was consistent with those of more recent studies.
authors.affiliation: National Center on Birth Defects and Developmental Disabilities, Centers for Disease Control and Prevention (F-15), 4770 Buford Hwy NE, Atlanta, GA 30341, USA. mxy1@cdc.gov
authors.forename: Marshalyn
authors.initials: M
authors.lastname: Yeargin-Allsopp
authors.forename: Catherine
authors.initials: C
authors.lastname: Rice
authors.forename: Tanya
authors.initials: T
authors.lastname: Karapurkar
authors.forename: Nancy
authors.initials: N
authors.lastname: Doernberg
authors.forename: Coleen
authors.initials: C
authors.lastname: Boyle
authors.forename: Catherine
authors.initials: C
authors.lastname: Murphy
mesh_terms: D001741:Black or African American; D020817:Asperger Syndrome / Q000175:diagnosis / Q000453:epidemiology; D001321:Autistic Disorder / Q000145:classification / Q000175:diagnosis / Q000453:epidemiology*; D002648:Child; D002675:Child, Preschool; D003071:Cognition; D005260:Female; D005845:Georgia / Q000453:epidemiology; D006801:Humans; D008297:Male; D011159:Population Surveillance; D015995:Prevalence; D012959:Socioeconomic Factors; D014481:United States / Q000453:epidemiology; D014505:Urban Population; D044465:White People