http://www.census.gov/hhes/www/povmeas/papers/famhh3.html

This analysis discusses the existing options and offers a conceptually more refined alternative: the "family/couple/household" (FCH) unit, which assumes income pooling among family members, including cohabiting couples, but not among non-relatives, and takes into account the benefits from economies of scale for all household members. Poverty rates are estimated using alternative definitions. Overall, empirical results show modestly lower poverty rates when household-level economies of scale are taken into account. The difference is largest for persons living in nontraditional household arrangements, such as cohabitors and non-family members.