Prevalence of intellectual disability among adults born in the 1980s and 1990s in the United States

Background: Prevalence of intellectual disability (ID) is currently estimated through parent report on surveys of children. It is difficult to estimate the number of adults living with ID in the United States because no comprehensive survey or surveillance allows for identification. The purpose of this study was to estimate the prevalence and number of adults with ID born between 1980 and 1999 using multiple years of the National Health Interview Survey (NHIS) and Census data. Methods: We concatenated the NHIS from 1997–2016 that evaluated parental response about whether a child aged 3–17 years had an ID. Using weighted survey analyses, we estimated the prevalence of ID among individuals across four birth cohorts—(1) 1980–1984, (2) 1985–1989, (3) 1990–1994, and (4) 1995–1999. The number of adults with ID was then extrapolated by applying these prevalence rates to Census population estimates (as of 1 July 2021) of respective birth cohorts. Results: Weighted prevalence of ID varied by birth cohort, sex, race and ethnicity, and US Census Bureau regions. The overall prevalence rate was 1.066 [95% confidence interval (CI): 0.831–1.302] for adults born between 1980 and 1984, 0.772 (CI: 0.654–0.891) for adults born between 1985 and 1989, 0.774 (0.675–0.874) for adults born between 1990 and 1994, and 1.069 (CI: 0.898–1.240) for adults born between 1995 and 1999. Overall, we estimate that 818 564 adults with ID who were approximately 21–41 years were living in the United States as of 2021. Conclusions: This study provides researchers examining adult health outcomes with an estimated denominator of young and middle-aged adults living with ID in the United States. Policymakers can use this information to support justification for resource and service needs, and clinicians may benefit from understanding that ID is a lifelong developmental condition often with additional physical, emotional and developmental needs requiring tailored care.