Objectives: From the two independent NSCH samples, we examined ASD prevalence in children who were US-born between 1990-2000. We assessed prevalence differences across surveys both by child age at survey and within one-year birth cohorts.
Methods: In the 2003 NSCH, prevalent cases were based on parental report of an “autism” diagnosis sometime during the child’s life. In the 2007 NSCH, question verbiage was revised and expanded. Thus, prevalence was defined two ways: parental report of an “ASD” during the child’s life and parental report of ASD currently. Estimates were weighted to be nationally representative of US-born children in various years.
Results:
In 2003, children aged 7-8 years had the highest “autism” estimates (10/1,000 children). Much lower estimates were observed for children aged 3-6 years (prevalence range 3-5/1000) and 11-13 years (prevalence range 4-6/1000). In 2007, children aged 5-13 years all had notably higher age-specific prevalence estimates of both “ever ASD” (prevalence range 18-29/1000) and “current ASD” (range 12-17/1000) than the “ever autism” estimates for children of comparable ages in 2003.
For children in each of the 1997-2000 birth cohorts (which includes children ages 3-6 years in 2003), relative differences between 2003 and 2007 estimates were 300%- 600% when comparison was based on the 2007 “ever ASD” definition and 200%- 400% when based on the 2007 “current ASD” definition. For children in the 1990-1996 birth cohorts (which includes children ages 7-13 years in 2003), the relative differences between 2003 and 2007 estimates were lower but still >100% for 5 of 6 cohorts when comparison was based on the 2007 “ever ASD” definition and >80% for 3 cohorts when based on the 2007 “current ASD” definition. (p<0.10 for all of these differences and p<0.05 for most)
Conclusions: Prevalence differences within birth cohorts are likely partially attributable to survey question changes. However, the magnitude of most differences suggests that continuing identification of children with ASDs between surveys was sizable, even among the oldest children, 7 years or older in 2003.
See more of: Epidemiology
See more of: Prevalence, Risk factors & Intervention