None of the identified research studies targeting low-income populations analyze nationally representative data sets. Study populations include both clinical and nonclinical research samples. Both the quantitative and qualitative studies draw on diverse geographical samples ranging from multiple sites in different states to specific low-income neighborhoods. Study samples include patients who are recruited from a range of health delivery settings (e.g., urban hospitals, prenatal clinics, community health centers), have particular diseases or health conditions (e.g., pregnancy, depression, cancer), and/or are members of specific demographic groups (e.g., elderly populations, African American women). The definition of low-income varies among studies and includes individual incomes; residence in a low-income community; participation in means-tested social programs such as Temporary Assistance to Needy Families (TANF), Women, Infants and Children Program (WIC) or Supplemental Security Income (SSI); and/or receipt of services from community-based organizations that serve low-income populations such as the homeless.