What does "universe" mean in the ATUS-X variable descriptions?

What does “universe” mean in the ATUS-X variable descriptions?

The universe is the population at risk of having a response for the variable in question. In most cases these are the households or persons to whom the question was asked. For example, only people who are employed are asked questions about their earnings on the job. Cases that are outside of the universe for a variable are labeled “NIU” in the codes and frequencies sections of the variable descriptions.

The universes typically take one of four forms:

All ATUS respondents: Variables with this universe (or some variant) were collected at the time of the ATUS interview and are only available for the one person in each household who responded to the ATUS.

All ATUS respondents and their household members: Variables with this universe (or some variant) are available for all individuals who were in the household at the time of the ATUS interview; these include RELATE, SEX, and AGE.

All Current Population Survey (CPS) household members: Variables with this universe (or some variant) are available for all individuals who were in the household at the time of the CPS interview, which occurred 2-5 months prior to the ATUS interview.

All ATUS (or CPS) households: Variables with this universe (or some variant) are available for all households in the survey indicated.

The universes will not always be entirely clean of apparently erroneous cases. Some people or households that should not have answered the question will have done so, and some that should have answered may be included in the “NIU” (not in universe) category. With the exception of the variables we construct for the convenience of users, these errors reflect problems in the original data.