Welcome! This guide was designed for the "Census Basics" Workshop at UVA Library, Fall 2019.
These are your learning outcomes:
Do you still have questions? I invite you to schedule a one-on-one consultation!
The two most commonly used Census surveys are the Decennial Census and the American Community Survey.
The Decennial Census is conducted every 10 years; the most recent one was in 2020. The Census attempts to count the entire US population (including households and group quarters). You can get only the most general population characteristics from the decennial Census. The Census aids in apportioning congressional districts and determining federal funding for local programs. The main purpose is a relatively simple count of population.
The American Community Survey (ACS) is conducted on a rolling basis. It has a lot more in common with survey estimates rather than a complete population count. Only some people are surveyed at any given time -- about 1% of the US is surveyed each year. There are 1-year and 5-year estimates available. They have strengths and weaknesses in regards to geography size, timelineness, statistical error, and ease of interpretation.
|ACS 1-Year (incl. Supplemental Tables)
|Point-in-time (April 1 of years ending in 0)
|12 month continuous survey
|60 month continuous survey
|2010 Decennial Census
|2017 ACS 1-year estimate
|2013-2017 ACS 5-year estimate
|Census block and larger
Geographies with populations >65,000
Note that Supplemental, "high-level" tables are available for populations with >20,000 people (e.g., City of Charlottesville) starting in 2014.
|Census tract and larger
|Counts every person
|Smaller sample size
|Larger sample size
|Margin of Error
|Smallest margin of error, i.e. very reliable estimates
|Highest margin of error, i.e., least reliable estimates
|Margin of error smaller than 1-year estimate, i.e., more reliable than 1-year estimates
|Best used when
|When you are only interested in general population characteristics (count; age, sex, race)
|Currency is more important than precision; when you are working solely with large population geographies; when you need more-easily interpreted population data
|Precision is more important than currency; When you are working with less populous geographies (small-sized geographies or rural areas)
|Only available every 10 years (data age quickly); only most general population characteristics
|Not available for less-populated geographies; high margin of error
|5 year estimate is harder to interpret; margin of error can still be high for small geographies
Which survey should you use? Ask yourself these questions:
This handbook from the Census is an excellent reference for understanding the ACS: