Ensuring that every person in the United States is counted once, only once, and in the right place is a fundamental goal of the decennial census. For many decades, the Census Bureau has evaluated coverage in each census and documented that some people are typically missed in the census. These people are referred to as census omissions. The Census Bureau has also documented that some people are counted in the wrong place and found evidence that some people are counted more than once during the census. Both of these errors are referred to as erroneous enumerations.

These types of coverage issues may have been self-identified by respondents when they completed their initial 2010 Census forms. There were questions on the initial 2010 Census forms that attempted to identify census omissions and erroneous enumerations. Census omissions were identified by a question that asked if there were additional people staying at the housing unit who were not included in the housing unit’s population count. This question was referred to as the undercount question. There were four types of census omission categories that were mentioned in the undercount question:

• Children, such as newborn babies or foster children
• Relatives, such as adult children, cousins, or in-laws
• Nonrelatives, such as roommates or live-in baby sitters
• People staying at the housing unit temporarily