Age at First Identification of Autism Spectrum Disorder: An Analysis of Two US Surveys

Abstract

Objective: Evidence regarding the age at which autism spectrum disorder (ASD) is identified is essential for improving early detection, yet many extant studies have not applied time-to-event analyses, which account for statistical biases that arise from sampling in cross-sectional surveys by adjusting for child age at time of parental report. Our objective was to estimate age distributions for first identification of ASD in national parent surveys using time-to-event analyses.

Method: We conducted time-to-event analyses of responses to identical questions in the 2011 to 2012 National Survey of Children's Health (n = 95,677) and the 2009 to 2010 National Survey of Children with Special Health Care Needs (n = 371,617).

Results: Parents in both surveys reported that a minority of ASD cases were identified before age 3 years, and that one-third to one-half of cases were identified after 6 years. In both surveys, a majority of parents described their child's ASD severity as mild, and these parents reported the oldest age at identification (mean, 5.6 and 8.6 years). In contrast, parents who described their child's ASD as severe reported earlier age at identification (mean, 3.7 and 4.5 years). Time-to-event analyses yielded older estimates of age at identification than analyses based on raw distributions.

Conclusion: In two national surveys, a majority of parents of children with ASD reported identification after 3 years, when eligibility for early intervention services expires, and many reported identification of ASD after school age. Later identification of children with milder symptoms highlights the need for early screening that is sensitive to all forms of ASD, regardless of severity.

Keywords: age at diagnosis; autism spectrum disorder; epidemiology; mass screening; survival analysis.

Figure 1

Age of first identification among all parents who were told by a professional that their children had autism and reported current autism and reported a special health care need. Note: ASD = autism spectrum disorder.

Figure 2

Cumulative incidence of autism identification in two national surveys. Note: Solid lines represent the National Survey of Children’s Health (NSCH); dotted lines represent the National Survey of Children with Special Health Care Needs (NS-CSHCN). Blue lines depict autism spectrum disorder (ASD) described as mild; green lines depict ASD described as moderate; red lines depict ASD described as severe; black lines depict all ASD.