ADDM has collected data on a biennial cycle since 2000,
with period prevalence estimates available for even years during
2000–2008. Prevalence estimates of ASD in this report are
from the 2008 surveillance year. The 14 ADDM sites that
provided data for the 2008 surveillance year included a total
population of 337,093 children aged 8 years, which was 8.4%
of the total population of children aged 8 years living in the
United States in 2008 (43).