Where does the income data come from?
The data are the most current income statistics from the US Census Bureau.
Most folks are familiar with the US Census Bureau's Decennial Census (2010) that sends a survey out to all (ideally!) US households. But what's not as well known is that the US Census Bureau also collects data each year from a much smaller sample of US households. They use this annual data to produce a dataset called the American Community Survey.
The American Community Survey (or the ACS) is the ongoing, annual survey of the social, economic, housing, and demographic characteristics of the nation’s population. It is a survey of 3.5 million addresses and informs over $675 billion of Federal government spending each year. This dataset is released in 3 parts each year:
- 1 year Estimates for geographies with a total population of 65,000 or more
- 1 year Supplemental Estimates for geographies with a total population of 20,000 - 64,999
- 5 year Estimates for geographies with a total population of less than 20,000
A Short History of the American Community Survey
- 1790 - The first census was conducted and occurred every 10 years using one form to collect data.
- 1940 - The decennial census began using a short form for all households and a long form for a sample of households.
- 1990's - The long form data was recognized as becoming less and less current as the decade went on.
- 2005 - The ACS was implemented to collect data for all of America's communities each year.
ACS Data vs. Census Data
The most current data available from the US Census Bureau for zip codes/ZCTAs is from the American Community Survey's 2018 5 year estimates. The US Census Bureau has taken American Community Survey data collected in 2014, 2015, 2016, 2017 and 2018 and uses this data to produce demographic estimates for zip codes/ZCTAs for 2018. When the Census Bureau collects income data in 2014 and then uses that 2014 data to estimate the 2018 income, they adjust the income reported in 2014 to 2018 dollars to account for inflation.
At the bottom of all the zip code pages, there's a section called "About the Data" that has the full citations.
For even more exciting details about Census data, you can read the "Income in the Past 12 Months" section in the Census’ Subject Definitions document.