In 2004, the Medicaid-enrolled prevalence of ASD was 70.1 per 100,000, using all US children as the denominator. As hypothesized, counties in the highest quartile of per-student education spending had lower prevalence, suggesting the substitution of education and Medicaid-reimbursed services. Because the needs of children with ASD cross the boundary between education and healthcare, counties with fewer education resources may turn to Medicaid to pay for their services (Koppelman 2004
; Noel and Shreve 2006
; Parrish et al. 2004
; Rodman et al. 1999
). Counties with more students and those with a greater proportion of students receiving special education services (both measures of potential system stressors) tended to have greater Medicaid-enrolled prevalence, adding some evidence to this hypothesis.
Medicaid-enrolled ASD prevalence varied greatly as a function of other county characteristics. Even after adjusting for poverty, the proportion of Medicaid-enrolled children in the county was associated with prevalence. While states have considerable latitude in how they use Medicaid to fund healthcare services for children, our analysis included state as a fixed effect, meaning that our results represent variation within states. The observed association between Medicaid enrollment and ASD prevalence may be due to counties taking differential advantage of their state’s Medicaid policies, perhaps because of local knowledge or the availability of education or other resources unmeasured in this study. Alternatively, families may change county of residence to be closer to better healthcare resources. The finding that counties with more pediatricians and pediatric specialists per capita enrolled a greater proportion of children with ASD in Medicaid may be due to families moving to be closer to these resources or a higher prevalence of pediatric specialists resulting in more diagnosing.
Counties with a greater proportion of white residents had higher Medicaid-enrolled ASD prevalence, which is in line with previous findings about racial and ethnic disparities in the diagnosis of autism (Mandell et al. 2002
). Membership in a traditionally underserved minority group may play a more important role in accessing services than income, which was not associated with ASD prevalence. While there is no known difference in the population prevalence of ASD among ethnic groups, one study found that African American and Latino children meeting research criteria for ASD were much less likely than white children to be identified as such in their healthcare or education records (Mandell et al. 2009
). Researchers have hypothesized that physicians may be less likely to diagnose ASD among ethnic minorities; there may also be more stigma or other barriers associated with ASD and accessing publicly funded services among ethnic minority parents.
Interpretation of study findings are limited by a number of factors, primary among them that the ASD diagnosis in the Medicaid claims has not been validated. While its accuracy has not been specifically examined, Fombonne et al. (2004)
found 97% positive predictive value for chart diagnoses and a diagnosis of ASD administered by a trained research team, and Yeargin-Allsopp et al. (2003)
found that 98% of children with a chart diagnosis met research criteria for ASD A second limitation is the absence of other county variables (e.g., ASD-specific intervention resources, county-level administrative prevalence of autism in the special education system) that may relate to identification in the Medicaid system.
Despite these limitations, there are important implications related to these findings. Within states, counties appear to differ in how they take advantage of Medicaid policies. The impact of these different arrangements between Medicaid and education on the coordination, intensity and quality of care for children with autism has yet to be determined. When Medicaid and education resources both are tapped to provide services for children with ASD, it can increase the potential volume of care and range of services these children receive. On the other hand, a large body of research suggests that when multiple systems are responsible for providing related care to the same child, it can result in considerable gaps and inefficiencies in care (American Academy of Pediatrics 2002
; Dickens et al. 1992
; US Department of Health and Human Services 1999
Our findings also provide further evidence for the need for outreach to minority groups and clinicians working with them to improve recognition of the developmental differences associated with ASD. Our focus on the county—rather than the individual—as the unit of analysis suggests that outreach might be geographically as well as ethnically targeted.
The findings raise a number of questions, such as the potential for families’ small-area migration to obtain services, which could have significant economic consequences for counties. It also raises questions regarding how state Medicaid and education policies interact with local practices and resources in the use of publicly funded services for children with ASD. States take varied approaches to using Medicaid to address the needs of children with ASD, including different eligibility requirements and arrangements between Medicaid and Special Education (Fox et al. 1993
; Stahmer and Mandell 2007
). Even within states, difficulties in coordinating services across systems may deter local education authorities from drawing on available resources from other systems. Understanding these policies and their implementation at the local level will help different jurisdictions develop effective decision rules regarding the identification and care of children with ASD.