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Duration of limiting intellectual disability: Months

Codes and Frequencies

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For persons who have at least one activity limitation (LANY), and for whom mental retardation was reported as a condition causing any activity limitation (CLIMRET), CLIMRETMO reports the duration, in months, of the mental retardation.

Data on the duration of limiting mental retardation were collected via the question, "How long [have/has] [you/person] had [mental retardation]?" Respondents could answer this open-ended question using the time unit of their choice (i.e., days, weeks, months, or years). The original responses to the question are reported in two complementary variables, CLIMRETTP (which specifies the time unit) and CLIMRETNO (which reports the number of such units). For the NHIS public use files, the National Center for Health Statistics (NCHS) recoded the results from these two variables to create two other variables using standard time units: years (CLIMRETY) and groups of months (CLIMRETMO).


Beginning in 2011, the phrase "mental retardation" was replaced with the phrase "intellectual disability, also known as mental retardation" in the survey question associated with CLIMRETMO. Apart from this change in wording, the variable is completely comparable for 2002 forward.

Additionally, there is a change over time in the coding of "unknown" cases for CLIMRETMO.

Aside from these two changes, CLIMRETMO is completely comparable over time.


All "unknown" cases for this variable share a common first digit of "9." The meaning of the second digit following the 9 differs for 2001 versus 2002 forward. In the earlier period, the "unknowns" were categorized as:

  • Unknown number of days (IPUMS NHIS code 91)
  • Unknown number of weeks (IHIS code 92)
  • Unknown number of months (IHIS code 93)
  • Unknown number of years (IHIS code 94)
  • Unknown time with condition (IHIS code 95)

In the latter period, "unknowns" were categorized as:

  • Unknown-refused (IHIS code 97)
  • Unknown-not ascertained (IHIS code 98)
  • Unknown-don't know (IHIS code 99)

Analysts can achieve comparability across all years by combining codes with a common first digit of 9 into a single "unknown" category.


  • 1997-2018: Persons limited due to mental retardation.


  • 1997-2018