The U.S. Census Bureau provides two data sources used on this site: The U.S. Decennial Census and the American Community Survey (ACS).
Survey details
The Decennial Census is conducted once every ten years, and is intended to survey all households in the United States. The ACS is conducted continuously, and samples a smaller number of households to develop estimates for the population. ACS surveys collect more detailed information previously only available in the long-form Decennial Census, which ACS has replaced since 2005.
ACS data on the Vermont Community Profiles are obtained or derived from the ACS 5-year rolling estimates. For example, the 2016 ACS estimates are derived from surveys completed between 2012 and 2016. Although some of the Vermont Community Profile visualizations allow users to compare ACS estimates from different years, the Census Bureau cautions users about identifying year-to-year trends if estimates are based on overlapping 5-year periods.
Housing units
The Decennial Census and American Community Survey use households to collect data. According to the U.S. Census Bureau, a household includes all the people who occupy a housing unit. A housing unit is a house, an apartment, a mobile home, a group of rooms, or a single room that is occupied (or if vacant, is intended for occupancy) as separate living quarters. Separate living quarters are those in which the occupants live separately from any other people in the building and which have direct access from the outside of the building or through a common hall. The occupants may be a single family, one person living alone, two or more families living together, or any other group of related or unrelated people who share living arrangements.
A housing unit is classified as occupied if it is the current place of residence of the person or group of people living in it at the time of interview, or if the occupants are only temporarily absent from the residence for two months or less, that is, away on vacation or a business trip. If all the people staying in the unit at the time of the interview are staying there for two months or less, the unit is considered to be temporarily occupied and classified as “vacant.”
Geographies
Data from the U.S. Census Bureau is tabulated at various geographic levels, including the state, county, town, and village levels for Vermont. Villages are a subset of towns. The two geographies should not be added together, otherwise estimates/counts will be duplicated.
Understanding estimates and data reliability ratings
American Community Survey (ACS) estimates are accompanied by margins of error. The margin of error describes the amount of sampling error associated with a particular estimate resulting from the survey. The larger the margin of error relative to the value of the estimate, the less confidence we have that the estimated results are close to the true figures for the population. Some ACS data sets shared on the Vermont Community Profiles may have very large margins of error, especially for communities with small populations, or for small subsets of a population, due to the small sample size. Furthermore, it should be noted although the ACS is administered by trained professionals and questions are vetted thoroughly, the estimates rely on data reported by survey respondents, which could contain inaccuracies.
Note that since the Decennial Census is a count, there are no margins of error available. However, since the Census is a count of the actual population, the data is expected to be very reliable.
To help users make informed decisions when using the data on the profiles, we have developed a simple system of data reliability ratings to accompany ACS data points. These ratings are displayed when users hover over data points on the visualizations. The data reliability ratings are derived from the coefficient of variation (CV) between the ACS estimate and its margin of error. If the CV is less than or equal to 15, the data reliability rating is “Good”. CV's less than or equal to 30 are labeled “Fair”, and CV's greater than 30 are labeled “Use with caution”.
If a user encounters a data reliability rating of “Use with caution”, users are encouraged to critically evaluate whether the data seems plausible. Users can compare estimates with previous years, with neighboring geographies, or with county-level estimates where appropriate.
More resources
The U.S. Census Bureau publishes the guide Understanding and Using American Community Survey Data: What All Data Users Need to Know, which contains a more detailed overview on how ACS data can be used and how to judge the accuracy of ACS estimates. The Bureau also provides a Statistical Testing Tool for users who want to compare two ACS estimates.
At the bottom of each visualization we provide a short description of the relevant terms. For a more detailed description of survey terms, review the ACS 2019 Subject Definitions. Users can also access a copy of the 2019 ACS Survey to view how the questions were administered to survey respondents. Be aware that although the U.S. Census Bureau tries to keep the ACS as consistent as possible, some subject definitions have evolved over the years.
A full list of all ACS tables is also available from the Census Bureau.
