Background. Accurately estimating the prevalence of intellectual and developmental disabilities (ID/DD) in the United States remains a challenge, with reported rates varying widely (3%-17%) based on the definitions and data sources used. Administrative data, especially from Medicare and Medicaid claims, due to their broad population coverage and longitudinal structure, can be a valuable resource for identifying and monitoring the health of individuals with many conditions, including ID/DD. However, current tools like the Centers for Medicare & Medicaid Services’ Chronic Conditions Data Warehouse (CCW) condition flags for intellectual disabilities, autism spectrum disorders, and other developmental disabilities exclude many potentially relevant diagnoses, leading to substantial variation across federal and nonfederal research in International Classification of Diseases (ICD) diagnosis codes included in claims-based ID/DD definitions.

Objectives. In this brief, we present findings from a descriptive analysis of Medicare and Medicaid administrative data and discussions with a multidisciplinary technical expert panel (TEP) toward informing a future update to the CCW condition flags for ID/DD.