Federal and state agencies report substantially different prevalence rates for developmental disabilities in the United States, ranging from 3.1% to 17.3%, according to a narrative review published in JAMA Pediatrics. This represents a five-fold difference in estimates.
The review examines how intellectual disability (ID) and developmental disability (DD) are defined across different systems. ID requires significant limitations in both intellectual functioning and adaptive behavior that originate before age 18. DD, as defined by the Developmental Disabilities Assistance and Bill of Rights Act, requires a severe, chronic disability manifesting before age 22 that results in substantial functional limitations in three or more areas of major life activity: self-care, receptive or expressive communication, learning, mobility, self-direction, independent living, and economic self-sufficiency.
Analysis of National Health Interview Survey-Disability Supplement data found that among adults meeting ID and/or DD criteria, 28.0% met both ID and DD criteria, 24.3% met ID criteria but not DD criteria, and 47.7% met DD but not ID criteria.
The review identifies varying approaches to defining these populations across different systems. Administrative databases and health records typically use categorical definitions based on diagnostic codes, while population-based surveys often employ functional definitions focusing on limitations in daily activities.
In 2017, the Administration on Community Living launched the IDD Counts! initiative to establish and maintain accurate data on IDD prevalence in the U.S. and its territories. This cross-agency effort includes the Centers for Disease Control and Prevention, the Office of the Assistant Secretary for Planning and Evaluation, Centers for Medicare & Medicaid Services, and National Institutes of Health.
The authors note a "transition cliff" in reported IDD rates between adolescence and adulthood, which they attribute to different systems of identifying and supporting people with ID and DD in childhood versus adulthood. Rather than making specific recommendations for standardizing definitions, the authors call for productive dialogue to bring greater consistency to the field.
Full disclosures and author information are available in the published review.