evidence: Although we know little about specific causes, the available evidence suggests that the following may put children at greater risk for developing ASD: [...] Understanding the risk factors that make a person more likely to develop ASD will help us learn more about the causes. CDC is currently funding and working on one of the largest US studies to date, called Study to Explore Early Development (SEED). [...] CDC's Autism and Developmental Disabilities Monitoring (ADDM) Network has been estimating the number of 8-year-old children with ASD in the United States since 2000. ASD occurs in all racial, ethnic, and socioeconomic groups. It is more than 4 times more common among boys than among girls.