In determining the poverty status of families and unrelated individuals, the Census Bureau uses thresholds (income cutoffs) arranged in a two-dimensional matrix. The matrix consists of family size (from one person to nine or more people) cross-classified by presence and number of family members under 18 years old (from no children present to eight or more children present). Unrelated individuals and two-person families are further differentiated by age of reference person (RP) (under 65 years old and 65 years old and over).

To determine a person's poverty status, one compares the person's total family income in the last 12 months with the poverty threshold appropriate for that person's family size and composition (see example below). If the total income of that person's family is less than the threshold appropriate for that family, then the person is considered "below the poverty level," together with every member of his or her family. If a person is not living with anyone related by birth, marriage, or adoption, then the person's own income is compared with his or her poverty threshold. The total number of people "below the poverty level" is the sum of people in families and the number of unrelated individuals with incomes in the last 12 months below the poverty threshold.

Since ACS is a continuous survey, people respond throughout the year. Because the income questions specify a period covering the last 12 months, the appropriate poverty thresholds are determined by multiplying the base-year poverty thresholds (1982) by the average of the monthly inflation factors for the 12 months preceding the data collection. See the table in "Appendix A" titled "Poverty Thresholds in 1982, by Size of Family and Number of Related Children Under 18 Years (Dollars)," for appropriate base thresholds. See the table "The 2009 Poverty Factors" in "Appendix A" for the appropriate adjustment based on interview month.

For example, consider a family of three with one child under 18 years of age, interviewed in July 2009 and reporting a total family income of $14,000 for the last 12 months (July 2008 to June 2009). The base year (1982) threshold for such a family is $7,765, while the average of the 12 inflation factors is 2.22421. Multiplying $7,765 by 2.22421 determines the appropriate poverty threshold for this family type, which is $17,271. Comparing the familyincome of $14,000 with the poverty threshold shows that the family and all people in the family are considered to have been in poverty. The only difference for determining poverty status for unrelated individuals is that the person's individual total income is compared with the threshold rather than the family's income.

For various reasons, the official poverty definition does not satisfy all the needs of data users. Therefore, some of the data reflect the number of people below different percentages of the poverty thresholds. These specified poverty levels are obtained by multiplying the official thresholds by the appropriate factor. Using the previous example cited (a family of three with one related child under 18 years responding in July 2009), the dollar value of 125 percent of the poverty threshold was $ 21,589 ($ 17,271x 1.25). Income Deficit - Income deficit represents the difference between the total income in the last 12 months of families and unrelated individuals "below the poverty level" and their respective poverty thresholds. In computing the income deficit, families reporting a net income loss are assigned zero dollars and for such cases the deficit is equal to the poverty threshold. This measure provides an estimate of the amount, which would be required to raise the incomes of all poor families and unrelated individuals to their respective poverty thresholds. The income deficit is thus a measure of the degree of the impoverishment of a family or unrelated individual. However, please use caution when comparing the average deficits of families with different characteristics. Apparent differences in average income deficits may, to some extent, be a function of differences in family size.

This was determined by a "Yes" answer to the question, "Does this person have any of his/her own grandchildren under the age of 18 living in this house or apartment?" This question was asked of people 15 years of age and over. Because of the low numbers of persons under 30 years old living with their grandchildren, data were only tabulated for people 30 and over.

This question determines if the grandparent is financially responsible for food, shelter, clothing, day care, etc., for any or all grandchildren living in the household. In selected tabulations, grandparent responsibility is further classified by presence of parent (of the grandchild).

The answer refers to the grandchild for whom the grandparent has been responsible for the longest period of time. Duration categories ranged from less than 6 months to 5 or more years.

This set of questions was added to the American Community Survey in 1999 to comply with legislation passed in the 104th Congress requiring that the decennial census program obtain information about grandparents who have primary responsibility for the care of their grandchildren. The response categories for length of time caring for grandchildren were modified slightly between the 1999 and 2000 American Community Survey questionnaires to match the 2000 decennial census questionnaire. The question has remained unchanged since then.

Before 2006, ACS grandparents data had a universe of people in households (which was the same as that in Census 2000 and the CPS). Beginning in 2006, the population in group quarters (GQ) is included in the ACS. Some types of GQ populations may have grandparents as caregivers distributions that are different from the household population. The inclusion of the GQ population could therefore have a noticeable impact on the grandparents as caregivers distribution. This is particularly true for areas with a substantial GQ population.

The data on grandparents as caregivers can be compared to previous ACS years, Census 2000, and to similar data collected in the CPS (with the potential limitation noted above about areas with a substantial GQ population).