A family consists of 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 householders family in 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 tabulations. Not all households contain families since a household may be comprised of a group of unrelated people or of one person living alone-these are called nonfamily households. Same-sex unmarried partner households are included in the family households category only if there is at least one additional person related to the householder by birth or adoption. Families are classified by type as either a husband-wife family or other family according to the sex of the householder and the presence of relatives. The data on family type are based on answers to questions on sex and relationship.

Average family size is a measure obtained by dividing the number of people in families by the total number of families (or family householders). In cases where the measures people in family or people per family are cross-tabulated by race or Hispanic origin, the race or Hispanic origin refers to the householder rather than the race or Hispanic origin of each individual. Nonrelatives of the householder living in family households are not counted as part of the family. They are included in the count of average household size. Average family size is rounded to the nearest hundredth.