Current procedures are based primarily on U.S. Bureau of the Census rules (1988). Its definition is "a family or household requires the presence of at least two persons: the householder and one or more additional family members related to the householder by birth, adoption, or marriage." Any householder living alone or exclusively with persons who are not related are defined as living in a "non-family household." By this definition, all cohabiting couples are excluded from family statistics. Under these rules, to avoid a sex bias, any adult member of the household who responds may be designated as the householder.