What does "universe" mean in the NAPP variable descriptions?

What does “universe” mean in the NAPP 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 census question was asked as reflected on the census questionnaire. For example, children are not usually asked employment questions, and men and children are not asked fertility questions. In some instances the universe suggested by the census questionnaire is not accurate. However, because of post-enumeration data processing, NAPP empirically verifies universes to obtain the most accurate statement possible of the universe. In some cases, there is no independent information in a sample to verify a universe.

Cases that are outside of the universe for a variable are labeled “NIU (not in universe)” on the codes page. Differences in a variable’s universe across samples are a common data comparability issue.

The universes will not always be free of apparently erroneous cases. Some persons or households that should not have answered the question did, and some that should have answered may be included in the “NIU” category. But until we perform comprehensive data editing and allocation, we do not know whether the variable in question is in error, or whether the variables that define the universe (for example, age or employment status) are incorrect.

Additionally, users should note the following definitions of the universe for each particular country:

Canada: Individual-level data on the Indian population in the territories is not available. The published census volumes provide aggregate information on these populations who were not individually enumerated. Thus, the published population totals for Canada in 1881 exceed the number of individuals in the 1881 Canadian census data file.

Great Britain: The census includes the population of England, Wales and Scotland; including “Islands in the British Seas” (viz. the Channel Islands and the Isle of Man). Ireland is not included.

Iceland: When released, the census will include the population of the main island of Iceland, and off-shore islands.

Norway: The census includes the complete population of Norway, including indigenous minorities in the three northern provinces of Troms, Finnmark and Nordland.

United States: All states, territories that eventually became states, and the District of Columbia, are included. However, the census enumeration excluded “Indians not taxed,” and thus does not contain Indian Territory, contiguous with the present-day state of Oklahoma. Alaska and Hawaii were also excluded from the enumeration.