Aggregate income is the sum of all incomes for a particular universe. Aggregate income is subject to rounding, which means that all cells in a matrix are rounded to the nearest hundred dollars. (For more information, see "Aggregate" under "Derived Measures".)

In compiling statistics on family income, the incomes of all members 15 years old and over related to the householder are summed and treated as a single amount. Although the family income statistics cover calendar year 1999, the characteristics of individuals and the composition of families refer to the time of enumeration (April 1, 2000). Thus, the income of the family does not include amounts received by individuals who were members of the family during all or part of calendar year 1999 if these individuals no longer resided with the family at the time of enumeration. Similarly, income amounts reported by individuals who did not reside with the family during 1999 but who were members of the family at the time of enumeration are included. However, the composition of most families was the same during 1999 as at the time of enumeration.

The terms "worker" and "work" appear in connection with several subjects: employment status, journey-to-work, class of worker, and work status in 1999. Their meaning varies and, therefore, should be determined by referring to the definition of the subject in which they appear. When used in the concepts "Workers in Family," "Workers in Family in 1999," and "Full-Time, Year-Round Workers," the term "worker" relates to the meaning of work defined for the "Work Status in 1999" subject.

A family includes a householder and one or more other people living in the same household who are related to the householder by birth, marriage, or adoption. All people in a household who are related to the householder are regarded as members of his or her family. A family household may contain people not related to the householder, but those people are not included as part of the householder's family in census tabulations. Thus, the number of family households is equal to the number of families, but family households may include more members than do families. A household can contain only one family for purposes of census tabulations. Not all households contain families since a household may be comprised of a group of unrelated people or of one person living alone.

Families are classified by type as either a "married-couple family" or "other family" according to the presence of a spouse. "Other family" is further broken out according to the sex of the householder. The data on family type are based on answers to questions on sex and relationship that were asked on a 100-percent basis.