Appendix for Prevalence and Characteristics of Autism Spectrum Disorder Among Children Aged 4 Years — Early Autism and Developmental Disabilities Monitoring Network, Seven Sites, United States, 2010, 2012, and 2014

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Appendix : Detailed Method for Estimating Surveillance Area Population Size of Partial Counties

For 2010, the number of children aged 4 years by sex and race/ethnicity was obtained for each census tract in the county from the 2010 decennial census counts. Next, each census tract was matched to the school district or districts to which it was fully or partially allocated, using the MABLE/Geocorr12: Geographic Correspondence Engine provided by the Missouri Census Data Center ( A list of excluded or partially excluded census tracts was compiled, and the number of children aged 4 years living in these census tracts was subtracted from the overall and sex- and race-specific total numbers of children in the county. For census tracts that were partially allocated to a school district, weighting was based on the 2010 census population of the county. Finally, population counts of children aged 4 years in each specific census race/ethnicity category (white, black, American Indian/Alaska Native, Asian/Pacific Islander, other race/ethnicity, multiracial, and Hispanic) were adjusted to the distribution of the National Center on Health Statistics (NCHS) bridged-race category counts for the county, thereby incorporating children categorized in the census counts as multiracial or other race into the bridged-race categories reported by NCHS (white, black, Hispanic, American Indian/Alaska Native, and Asian/Pacific Islander). The same methods were used to estimate the prevalence of ASD among children aged 8 years living in the Early ADDM Network surveillance area.

For the nondecennial census years 2012 and 2014, denominators for sites that covered less than a full county were estimated by using school enrollment counts for the appropriate grades in the covered area and applying the distribution of these counts to the county-level bridged-race postcensal population estimates from NCHS (



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