Original Paper

Social Psychiatry and Psychiatric Epidemiology

, Volume 45, Issue 3, pp 319-327

First online:

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

  • M. PosserudAffiliated withCentre for Child and Adolescent Mental Health, Unifob Health Email author 
  • , Astri J. LundervoldAffiliated withDepartment of Biological and Medical Psychology, Faculty of Psychology, University of Bergen
  • , Stein Atle LieAffiliated withCentre for Child and Adolescent Mental Health, Unifob Health
  • , Christopher GillbergAffiliated withChild and Adolescent Psychiatry, University of Gothenburg

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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.


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.


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.


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%.


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.


Autism spectrum disorders Prevalence Non-response bias Diagnostic instrument Assessment method