The prevalence of autism spectrum disorders: impact of diagnostic instrument and non-response bias

Soc Psychiatry Psychiatr Epidemiol. 2010 Mar;45(3):319-27. doi: 10.1007/s00127-009-0087-4. Epub 2009 Jun 24.

Abstract

Background: A large part of the variability in rates of autism spectrum disorders (ASD) across studies is non-aetiologic, and can be explained by differences in diagnostic criteria, case-finding method, and other issues of study design.

Aim: To investigate the effects on ASD prevalence of two methodological issues; non-response bias and case ascertainment. We compared the findings of using a semi-structured parent interview versus in-depth clinical assessment, including an ASD specific interview. We further explored whether including information on non-responders affected the ASD prevalence estimate.

Method: A total population of 7- to 9-year olds (N = 9,430) was screened for ASD with the autism spectrum screening questionnaire (ASSQ) in the Bergen Child Study (BCS). Children scoring above the 98th percentile on parent and/or teacher ASSQ were invited to participate in the second and subsequently in the third phase of the BCS where they were assessed for ASD using the Development and Well-Being Assessment (DAWBA), and the Diagnostic Interview for Social and Communication disorders (DISCO), respectively.

Results: Clinical assessment using DISCO confirmed all DAWBA ASD cases, but also diagnosed additional cases. DISCO-generated minimum prevalence for ASD was 0.21%, whereas estimated prevalence was 0.72%, increasing to 0.87% when adjusting for non-responders. The DAWBA estimate for the same population was 0.44%.

Conclusion: Large variances in prevalence rates across studies can be explained by methodological differences. Both information about assessment method and non-response are crucial when interpreting prevalence rates of ASD.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Asperger Syndrome / diagnosis
  • Asperger Syndrome / epidemiology
  • Asperger Syndrome / psychology
  • Autistic Disorder / diagnosis
  • Autistic Disorder / epidemiology
  • Autistic Disorder / psychology
  • Bias
  • Child
  • Child Development Disorders, Pervasive / diagnosis*
  • Child Development Disorders, Pervasive / epidemiology
  • Child Development Disorders, Pervasive / psychology
  • Data Collection / statistics & numerical data
  • Female
  • Humans
  • Longitudinal Studies
  • Male
  • Mass Screening / statistics & numerical data
  • Neuropsychological Tests
  • Prevalence
  • Psychiatric Status Rating Scales / statistics & numerical data
  • Psychometrics
  • Reproducibility of Results
  • Research Design
  • Surveys and Questionnaires
  • Teaching / statistics & numerical data