Demographic D.4 Low-income households


Descriptive Title:

Proportion living at or below 200% of the Census poverty threshold


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. 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.

Since American Community Survey (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. In 2009 the poverty threshold for two adults and a child under 18 was $17,268 ( Becuase San Francisco and the Bay Area has a higher than average cost of living we chose to examine the percent of persons living at or below 200% of the poverty threshold, which would have been $34,536 for the same family in 2009.

The equation used to determine percent below the poverty level is: Percent in poverty = Total persons at or below 200% of the poverty level / Total population with poverty status determined.

In the Percent of Population Living at or Below 100% of the Census Poverty Threshold graph, the Hispanic / Latino category is not a mutually exclusive race category. In the ACS, race and Hispanic origin are treated as separate concepts with a separate question asking about Hispanic origin. Hispanics or Latinos are people who classified themselves in at least one of the specific Spanish, Hispanic, or Latino census categories. People of Hispanic origin may also be of any race, and are asked to answer a race question by marking one or more race categories, including: White, Black or African American, American Indian or Alaska Native, Asian, Native Hawaiian or Other Pacific Islander, and Some Other Race. Thus, the listed races such as Asian or Black/African American, may include some persons who identify as Hispanic. In order to better demostrate disparities in povery by race, non-Hispanic whites are included as a mutually exclusive race category.

The ACS is a sample survey, and thus, data are estimates rather than counts. Estimates have accompanying margins of error that indicate the span of values that the true value could fall within. Margins of error should be subtracted from and added to the value to determine the range of possible values. If the margin of error is too big relative to the value, data are not shown because they are statisitcally unstable. A coefficient of variation of 30% was used to determine statistical instability.