Functional limitation is based on six questions asked of people aged 18 and over in the National Health Interview Survey (NHIS):
- Do you have difficulty seeing, even when wearing glasses?
- Do you have difficulty hearing, even when using your hearing aid(s)?
- Do you have difficulty walking or climbing steps?
- Using your usual language, do you have difficulty communicating, for example, understanding or being understood?
- Do you have difficulty remembering or concentrating?
- Do you have difficulty with self-care, such as washing all over or dressing?
The response categories are: no difficulty, some difficulty, a lot of difficulty, and cannot do at all/unable to do. These questions have been asked annually in NHIS starting in 2010 and are found in the 2010 Quality of Life NHIS files, the 2011–2017 Functioning and Disability NHIS files, and the 2018–2019 Sample Adult files. Respondents with answers to one or more of the six questions are classified into one of three mutually exclusive categories. Those responding “a lot of difficulty” or “cannot do at all/unable to do” to at least one question are classified in the “a lot of difficulty/cannot do at all” category. Of the remaining respondents, those responding “some difficulty” to at least one question are classified in the “some difficulty” category, and those responding “no difficulty” to all questions are classified in the “no difficulty” category. During 2010–2019, 0%–8% of respondents were excluded from analysis because they were missing data across all six functioning questions. Data are for the U.S. civilian noninstitutionalized population. For more information on functional limitation, see the Washington Group on Disability Statistics at: http://www.washingtongroup-disability.com/ and the “Statement of rationale for the Washington Group general measure on disability” at: https://www.cdc.gov/nchs/data/washington_group/rationale.pdf.
Beginning with Health, United States, 2017, this measure of functional limitation replaces the disability measure used in earlier editions of Health, United States. While both measures assess difficulty in several areas of functioning, they are not comparable.
For more information about NHIS, including the annual questionnaire and documentation for these files, see: https://www.cdc.gov/nchs/nhis/data-questionnaires-documentation.htm.