Poverty rate methodology

Using publicly available data, The Times computed poverty rates for the approved Los Angeles Promise Zone and two alternative zones following the U.S. Department of Housing and Urban Development methodology detailed below.

The Times first identified all census tracts entirely or partially within the Los Angeles Promise Zone. For partial tracts, The Times apportioned the population and households based on block-level counts from the 2010 census. Poverty rates were calculated for each census tract with data from the 2006-2010 American Community Survey five-year estimates. For the rate of extremely low-income households, The Times downloaded the U.S. Census Bureau’s Comprehensive Housing Affordability Strategy (CHAS) special tabulation posted on the HUD website.

The Times was unable to exactly match the HUD methodology because the CHAS data available for download provided extremely low-income household data by census tract. HUD had access to the data by block group. The smaller geographies reduce the error in adjusting for block groups split by the promise zone boundaries. The Times calculated the poverty rate for the Los Angeles Promise Zone as 34.2%, about 2% lower than the HUD figure.

To calculate poverty rates for its alternate zones, The Times compiled areas of about 165,000 — the population of the Los Angeles Promise Zone — using only whole census tracts so that no apportionment was necessary.

HUD explains its methodology as follows:

The data source used in the optional Promise Zones mapping tool is the concentration of people in poverty, which is calculated with data at the block group level from American Community Survey (2011) for metropolitan areas and the tract level for non-metropolitan areas. This indicator represents the percent of people within the target geography who are below the poverty line. The estimated concentration of Extremely Low Income (ELI) households represents an approximation of the percent of households within the specified area whose household combined income is below 30% of the HUD defined Area Median Income (AMI). This ELI indicator is calculated with data from the block group level from CHAS 2010. The final “poverty rate” for purposes of Promise Zone eligibility is the greater of these two indicators.

HUD’s mapping tool overlays the locally defined neighborhood/community boundaries with data associated with that area and estimates the rates of certain indicators in that area using a proportional allocation methodology. For metropolitan areas, the tool uses census block group (as defined for census 2010) as the smallest statistical boundary for the available data. For non-metropolitan areas, the tool uses census tract data to account for less precision in low-population areas. If the locally defined neighborhood/community is partially within two different census areas, the data for each factor or threshold criteria are calculated based on the portion of the 2010 housing units located in each census area for the vacancy variables and 2010 population for the population, poverty and employment variables. The 2010 housing unit and population count data are available to HUD at the block level and thus can be used as the underlying data to apportion each block group and tract’s appropriate share of importance.

For the Promise Zone boundary submitted by the city of Los Angeles, the mapping tool assigned each block group within the zone the greater of the poverty rate or the ELI rate for that block group. The mapping tool then averaged the poverty/ELI rates for all of the block groups, weighted by the portion of the  population of each block group that is within the zone. This provided an overall poverty/ELI rate for the city of Los Angeles Promise Zone of 34.86%.