Brief report: diminishing geographic variability in autism spectrum disorders over time?

We investigated differences in the geographic distribution of autism spectrum disorders (ASD) over time in central North Carolina with data from the Autism and Developmental Disabilities Monitoring Network. Using generalized additive models and geographic information systems we produced maps of ASD risk in 2002–2004 and 2006–2008. Overall the risk of ASD increased 52.9 % from 2002–2004 to 2006–2008. However, the magnitude of change in risk was not uniform across the study area; while some areas experienced dramatic increases in ASD risk(>400 %), others experienced slight decreases. Generally,areas with the lowest risk in 2002–2004 experienced the greatest increases over time. Education and outreach efforts in North Carolina expanded during this period, possibly contributing to the observed leveling of risk over time.