Autism incidence in California, 1992-2010

The incidence of autism in the United States has risen steadily over the past few decades. The most recent widely cited estimate of the prevalence rate of Autism Spectrum Disorders is from 2006 and is one in every 110 children aged eight years. Whether the incidence of autism has continued to increase, remained stable, or even decreased since 2006 is currently not known. We estimate the incidence rate for autism in the state of California for the years 1992 through 2010 by linking the state's Birth Master Files to the Department of Developmental Services' annual autism caseload records. We then examine the demographic and socioeconomic composition as well as the developmental functioning of those who were diagnosed during the study period. We determine whether the groups of children diagnosed in each year vary by sex or age or by maternal age at birth, race/ethnicity, education level, Medi-Cal status, or place of birth. During the study period, the incidence of autism among children three through nine years old in California rose between 1992 and 2008 but then remained stable from 2008 to 2010. The odds ratios of being diagnosed with autism among Hispanic children and those on Medi-Cal have increased in recent years. Meanwhile, although those with at least a high school education still have higher odds ratios of diagnosis relative to those with less than a high school education, the gap is decreasing. Our results indicate a considerable shift in the demographic composition of children with autism.