From each of the databases described above, the population of children with disabilities was identified. All children under the age of 18 at the beginning of state fiscal years 1990-1994 were identified as disabled if they were receiving services through special education, the Department of Mental Health and Developmental Disabilities (DMEDD) inpatient treatment, Assistance for the Aged, Blind and Disabled (AABD) disability programs, or Medicaid reimbursed services. Because individual level data on SSI receipt was only available to us for very recent time periods, children receiving AABD were used to approximate the SSI population in Illinois over the five fiscal years.1
Disability identification was based solely on program participation for children in special education, AABD, and DMH. The Medicaid reimbursed services data, however, contains data on services provided for preventative and well-child care as well as for the more serious inpatient and rehabilitative services. Identifying "disabled children" in this service data was not a straight-forward task. In order to use the least restrictive definition of disability, we selected children who demonstrated a disabling condition in one of three ways. First, we selected all children who had a non-institutional claim containing an ICD-9-CM (International Classification of Diseases Clinical Modification) diagnosis code that indicated a disabling condition according to the Social Security disability evaluation standards.2 Second, we selected all children who received a service under a category of service that indicated a special need. Finally, provider types that were associated with disabling conditions or conditions requiring rehabilitation were selected. A detailed description of the ICD-9-CM diagnosis codes used to map to the Social Security Administration's listing of disabling conditions can be found in Appendix A.
Each of the selection methods was designed to identify children eligible for SSI under the most current disability evaluation standards. We recognize that disability determination in children is a complex evaluation that does not depend on diagnosis or program service alone. We expect that our selection criteria err on the side of overestimating the disabled population. Throughout the analysis, the utilization of "Medicaid services" will refer only to Medicaid reimbursed services that indicate a disabling condition as defined by our selection criterion. Likewise, children referred to as participating in the Medicaid program will refer only to children receiving services specified in our selection criterion.
A description of the disabling conditions, categories of service, and provider types that we used in the selection and their prevalence can be found in table 1. Two of the ICD-9-CM diagnoses that are included in the selection were associated with a few restrictions. Asthma, for example, was only used identify a child as disabled when it was accompanied by two or more hospitalizations or three or more emergency room visits. Epilepsy was similarly conditioned on the presence of a hospitalization or three or more emergency room visits within the fiscal year. Inpatient hospitalizations (general, psychiatric, and rehabilitative) also had conditions that were necessary for the disability determination in our selection. Three or more inpatient hospitalizations within a fiscal year or one hospitalization that lasted for 20 days or longer indicated disability in this analysis.
From the ICD-9-CM selection, the significant increase in the number of children that were identified after FY 1992 was due mainly to the increased prevalence of developmental speech or language disorders and other mental disorders. This increased "prevalence" however was primarily due to expanded service availability, particularly for mental health services. Two provider types, mental health service providers and local educational agencies, served significantly higher number of children after FY 1992. Most children were selected by the ICD-9-CM diagnosis code on a particular claim rather than the category of service or provider type. Over time the number of children that met the selection criteria by the ICD-9-CM diagnosis code and category of service also rose significantly (Table 2). This was more likely to happen as services became increasingly available for diagnoses that fell within our selection criterion.