In order to measure access to health care, I am using USUALPL variable. When I read the description about this variable on the website (nhis.ipums.org), I do not understand the responses reported under the “Code 0.” My understanding is that these are those respondents who do not need health care access. Am I right? If so, it will help to recategorize “USUALPL” variable as per my research interest.
The code USUALPL == 0 indicates “NIU” or Not in Universe. Basically, this indicates who in the sample the question applied to in the questionnaire. What this specifically indicates differs slightly depending on what sample of NHIS data you are using. The details of this can be found on the Universe Tab. For example, from 1997 - 2017 the universe statement is “sample adults age 18+ and sample children under age 18.” This means that only sample adults who are over the age of 18 and sample children who are under the age of 18 are asked this question. Everyone who does not meet these criteria are not asked this question.