Sustainable Communities Index

Demographic D.3 Per capita and household income

Descriptive Title: Per capita and median household income

Geographic Unit of Analysis: Census tract

Methods

Per capita income is the mean income computed for every man, woman, and child in a geographic area. It is derived by dividing the total income of all people 15 years old and over in a geographic area by the total population in that area. Income is not collected for people under 15 years old even though those people are included in the denominator of per capita income.

In contrast to per capita income, median household income presents an alternative picture of income distribution in San Francisco, accounting for the fact that many households pool their income. The neighborhood weighted median is calculated by using the estimate number of households that fall into household income ranges. More detailed methodology for recalculating medians and their margins of error for aggregated American Community Survey data is provided in the Map Methods documentation (http://www.thehdmt.org/data_map_methods.php).

The American Community Survey 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.

Data Source

American Community Survey (ACS), 5-year Estimates, 2005-2009.

Map and table created by San Francisco Department of Public Health, Environmental Health Section using ArcGIS software.

Map data is presented at the level of the census tract, which was calculated by assigning census block data to census tracts based on spatial location. The map also includes planning neighborhood names, in the vicinity of their corresponding census tracts.

Table data is presented by planning neighborhood. While planning neighborhoods are larger geographic areas than census tracts, census tracts do not always lie completely within a planning neighborhood. SFDPH chose to use the San Francisco Planning Department's census tract neighborhood assignments to calculate neighborhood values. This assignment method relies on a 'centroids within' methodology to convert census tracts to geographic mean center points. Census tracts are assigned to planning neighborhoods based on the spatial location of those geographic mean center points and calculated the planning neighborhood totals for the table.

Detailed information regarding census data, geographic units of analysis, their definitions, and their boundaries can be found in the SCI at the following links:

https://SustainableSF.org/etc/Geographic_Units_of_Analysis.pdf

https://SustainableSF.org/data_map_methods.php