The Prevalence of Autism Spectrum Disorder in School Aged Children: Population Based Screening and Direct Assessment
Objectives: To determine prevalence of ASD in school-aged children born in 2004 using population-based screening and direct assessment.
Methods: Children born in 2004 and living in a contiguous geographic region (census derived n=8780) were screened for ASD using the Social Communication Questionnaire. The demographics of the catchment area for the target age group are 57% Non-Hispanic White, 33% Non-Hispanic Black, 8% Hispanic, and 2% other. Screening was conducted in partnership with 123/127 private and public elementary schools. Partnerships were also established with 25 home-school associations and three virtual schools in the area. All children at risk for ASD, as well as a subset of those falling below the threshold for risk, were invited to participate in a developmental assessment to determine ASD case status. Diagnostic assessment procedures included parent interview, parent and teacher behavior checklists, IQ and adaptive measures, and the Autism Diagnostic Observation Schedule, Second Edition. Clinical diagnoses were assigned by doctoral level clinicians, and were based on lifetime history of ASD symptoms. Prevalence estimates with 95% CI were calculated based on the NCHS vintage 2014 census population estimates. To account for the complex multi-phase design, multiple sampling weights with raking procedures were computed to account for the differentials in the probability of selection between strata, differences in non-response, and sampling frame adjustments in the final weighted estimate.
Results: Approximately 48% of eligible children participated in the screening process (n=4185). Of children with complete screening data (n=3,698), 7.4% screened positive for ASD risk, and 23% fell in a sub-threshold range for ASD risk. Of eligible children invited for a diagnostic assessment (n=704), 41.5% completed this assessment (n =292). ASD prevalence in this sample is 3.62%. Males were more likely to have ASD than females (6.77:1). ASD prevalence was higher among white children (3.92%) than black children (2.52%). Among those diagnosed, 21% had cognitive functioning falling in the Intellectually Disabled range, and 70% had delays in adaptive skill development (Vineland ABC<85). The majority of children meeting criteria for ASD (36/52; 69%) had received a formal clinical ASD diagnosis prior to entering the study. Of the 16 children newly identified via participation in the study, 14 had a prior neurodevelopmental/behavioral diagnosis such as ADHD, anxiety, language delay, etc. Six children (6/52; 12%) had a clear developmental history of ASD but did not display clinically significant symptoms at the time of participation in this study.
Conclusions: ASD prevalence in this study was substantially higher than has been previously reported by studies using records-based or administrative count methods to ascertain prevalence. Our study also revealed substantial functional impairment in the ASD group during the later elementary school years. Results suggest that some individuals with ASD may not be formally identified as such and may not be receiving the appropriate supports. However, 12% with a history of ASD no longer had significant ASD-related symptoms, providing further support for the potential for optimal outcomes in some individuals.