American Community Survey

The American Community Survey (ACS) is a nationwide survey from the U.S. Census Bureau that replaces the decennial census “long form” survey. Like the decennial long form it replaces, the ACS gathers information from a subset of the U.S. population. However, the ACS is conducted on a continual, monthly basis. This enables estimates from the ACS to be published every year, giving a more current view of the characteristics of the population and housing.

What Subjects Are Covered

The ACS collects information on a wide range of characteristics from a sample of persons and households in the U.S.:

Demographic (see a demographic sample)
- Age
- Sex
- Race and ethnicity
Social (see a social sample)
- Household composition and relationships
- Marital status and fertility
- School enrollment and educational attainment
- Place of birth
- Language spoken
- Ancestry
Economic (see an economic sample)
- Employment status, industry, and occupation
- Commuting to work
- Incomes and benefits
- Poverty
Housing (see a housing sample)
- Occupancy and tenure (owner or renter occupancy)
- Home value and monthly housing costs
- Other housing characteristics such as size of structure and year built

What Is Published

ACS data are combined over different time periods and published by the U.S. Census Bureau annually in three series. Please see the various tabs for more information.

1-year estimates
- Data collected over a 12-month period
- Only for areas with populations of 65,000+
- Smallest sample, less reliable, most current
- Best used when recent estimates are more important than precise estimates and analyzing large populations
3-year estimates
- Data collected over a 36-month period
- Populations of 20,000+
- Larger sample, more reliable, less current
- Best used when analyzing smaller populations
5-year estimates
- Data collected over a 60-month period
- All geographic areas down to census tract or block group level — Note that the 5-year estimates are the only ACS estimates available at a neighborhood scale
- Largest sample, most reliable, least current
- Best used when accuracy is more important than having recent estimates and analyzing very small populations

What You Need to Know

There are some important ideas to keep in mind when using ACS data and products:

Characteristics - ACS tells us about the characteristics of the population, not counts, because it is a done with a sample of the population.
Period Estimates - ACS estimates reflect the characteristics of the population and housing over the entire period of time the data were collected, not for any particular point in the period.
Margins of Error - ACS estimates carry margins of error which indicate how reliable the estimate is, with bigger margins of error signaling lower reliability.

To use the ACS responsibly, pay attention to margins of error and make a careful decision about whether the reliability of the estimates is high enough for your purposes.
- Margins of error can be quite large, especially for small areas and population groups.
- 1-year estimates generally have much higher margins of error than the multi-year estimates.
- Although more accurate, the 5-year estimates still tend to have higher margins of error than the decennial census long form estimates due to the lower sampling rates in the ACS
Comparing Estimates - making comparisons using ACS data is complicated.
- Differences in estimates may not reflect actual differences, margins of error need to be considered.
- Although the ACS and past decennial census long forms cover similar topics, estimates for some should only be compared with caution or not at all.

What Else You Should Know

For a more detailed discussion of the issues involved with using ACS data please see the ACS data issues tab at the top of this page.

1-Year Data Series

ACS data can provide a unique picture of local communities by providing information on indicators such as:

Household income levels
Age and education level of a population
Race and ethnic makeup of a community
How a population has changed over time

1-Year Estimates

The 1-year estimates for the City of Seattle provide the most current information available.

Data collected over a 12-month period
Available for:
- City of Seattle
- Five component PUMA’s (Map of PUMA’s in Seattle)
Smallest sample, less reliable, most current
Best used when:
- Currency is more important than precision
- Analyzing large populations

What Does Seattle Look Like?

2012 Narrative Profile

The Narrative Profile is a basic descriptive report about the social, economic, housing and demographic characteristics based on the 1-Year Data Series for a particular geographic area.

2013 Data Profile

This data series is published by the U.S. Census Bureau in four individual subject profiles (includes reports for the City of Seattle and all five PUMA’s in one PDF for each profile).

These profiles have been combined into one tabbed Excel file for each individual geography.

Caution: Please see the ACS data issues tab above for an understanding of the changes in population control totals for the 2010 series.

To access the full range of available ACS data products, visit the Census Bureau’s American FactFinder online data portal.

What is a PUMA?
There are five PUMAs (public use microdata areas) in Seattle. A PUMA is a decennial census area for which the U.S. Census Bureau provides specially selected extracts of raw data from a small sample (5-percent) of population and housing unit records. The data is from the American Community Survey and is screened to protect confidentiality. These extracts are referred to as ‘‘public use microdata sample’’ files. They allow you to create your own statistical tabulations and data summaries. PUMAs are delineated uniquely within each state and comprise areas that contain at least 100,000 people.

3-Year Data Series

This data series has been discontinued by the U.S. Census Bureau. Seattle will continue to receive one year and five year ACS products.

ACS data can provide a unique picture of local communities by providing information on indicators such as:

Household income levels
Age and education level of a population
Race and ethnic makeup of a community
How a population has changed over time

3-Year Estimates

Data collected over a 36-month period
Available for:
- City of Seattle
- Five component PUMA’s (Map of PUMA’s in Seattle)
Larger sample, more reliable, less current than 1-year estimates
Best used when:
- Analyzing smaller populations

What Does Seattle Look Like?

2010 – 2012 Narrative Profile

The narrative profile is a basic descriptive report about the social, economic, housing, and demographic characteristics based on the 3-Year Data Series for a particular geographic area.

2011 – 2013 Data Profile

This data series is published by the U.S. Census Bureau in four individual subject profiles (includes reports for the City of Seattle and all five PUMA’s in one PDF for each profile).

Caution: Please see the ACS data issues tab above for an understanding of the changes in population control totals for the 2010 series.

To access the full range of available ACS data products, visit the Census Bureau’s American FactFinder online data portal

What is a PUMA?
There are five PUMAs (public use microdata areas) in Seattle. A PUMA is a decennial census area for which the U.S. Census Bureau provides specially selected extracts of raw data from a small sample (5-percent) of population and housing unit records. The data is from the American Community Survey and is screened to protect confidentiality. These extracts are referred to as ‘‘public use microdata sample’’ files. They allow you to create your own statistical tabulations and data summaries. PUMAs are delineated uniquely within each state and comprise areas that contain at least 100,000 people.

5-Year Data Series

ACS data can provide a unique picture of local communities by providing information on indicators such as:

Household income levels
Age and education level of a population
Race and ethnic makeup of a community
How a population has changed over time

5-Year Estimates

The 5-year estimates for the City of Seattle provide the most reliable information available. These estimates are also the basis for the City’s individual neighborhood reports.

Data collected over a 60-month period
Available for:
- City of Seattle
- Five component PUMA’s (Map of PUMA’s in Seattle)
- City of Seattle Community Reporting Areas and Council Districts
  (only available for 2006 – 2010) - Visit our Neighborhoods tab on our About Us page for more information
- All geographic areas down to census block group (not provided through this website)
Largest sample, most reliable, least current of all estimate periods
Best used when:
- Accuracy is more important than having recent estimates
- Analyzing very small populations

What Does Seattle Look Like?

American Community Survey 5 Year Data Series Map Narrative Profiles are not provided for the 5-Year Data Series.

2009 – 2013 Data Profile

This data series is published by the U.S. Census Bureau in four individual subject profiles (includes reports for the City of Seattle and all five PUMA’s in one PDF for each profile).

These profiles have been combined into one tabbed Excel file for each individual geography.

Caution: Please see the ACS data issues tab above for an understanding of the changes in population control totals for the 2010 series.

To access the full range of available ACS data products, visit the Census Bureau’s American FactFinder online data portal

What is a PUMA?
There are five PUMAs (public use microdata areas) in Seattle. A PUMA is a decennial census area for which the U.S. Census Bureau provides specially selected extracts of raw data from a small sample (5-percent) of population and housing unit records. The data is from the American Community Survey and is screened to protect confidentiality. These extracts are referred to as ‘‘public use microdata sample’’ files. They allow you to create your own statistical tabulations and data summaries. PUMAs are delineated uniquely within each state and comprise areas that contain at least 100,000 people.

Data Issues

American Community Survey data provides the most in-depth picture of Seattle’s population and housing. ACS estimates need to be interpreted carefully and can be complicated to use so you should educate yourself on the basics of the ACS. The Census Bureau’s Compass Products can help you effectively use the ACS data while navigating the challenges involved.

It is very important to recognize that, as a sample survey, the American Community Survey provides information on the characteristics of the population – and is not meant to count the population. You should keep in mind that ACS estimates carry larger margins of error than decennial census sample estimates. This is especially true for small areas and population groups.

Know Your Estimate Series

Estimates from the ACS represent the characteristics of the population and housing over a period of time: 1 year, 3 years, or 5 years, depending on the estimate series. (For example, the 5-year ACS estimates provide a weighted average of ACS responses collected over 60 months.) Because ACS estimates are for a whole period of time, you cannot use ACS estimates to determine what is happening at any particular day, month, or year. This is crucial to keep in mind for periods with a great deal of change.

It is important to select the estimate series that best suits your needs. Depending on the desired geography, there may be up to three different estimates to choose from. Please click on their respective tabs above for more information:

1-year series
- Data collected over a 12-month period
- Populations of 65,000+
- Smallest sample, less reliable, most current
- Best used:
  - Currency is more important than precision
  - Analyzing large populations
3-year series
- Data collected over a 36-month period
- Populations of 20,000+
- Larger sample, more reliable, less current
- Best used:
  - Analyzing smaller populations
5-year series
- Data collected over a 60-month period
- All geographic areas down to census block group regardless of population size
- Largest sample, most reliable, least current
- Best used:
  - Precision is more important than currency
  - Analyzing very small populations

The U.S. Bureau provides an excellent presentation “Understanding Multi-Year Estimates from the American Community Survey” that gives guidance on how to choose an estimate series and how to use the data appropriately.

Population Control Totals

The first 5-year ACS data release is for 2005-2009 and provides geographic coverage all the way down to the block group level. It is important for you to know that the 2005-2009 ACS data are controlled to population and housing estimates that are based on Census 2000 counts.

The 2006-2010 5-year ACS data is controlled to Census 2010 population and housing counts. The 2006-2010 data is intended to replace the decennial census long-form data, although important differences exist. See below for information about comparing ACS data to the decennial census.

Margins of Error

All estimates that are based on samples, such as the ACS and the decennial census long-form estimates, include some uncertainty or “sampling error.” The margin of error is a measure of sampling error that helps to tell us the range within which the real value most likely falls.

Knowing the size of the margin of error is important because it helps you understand how reliable the estimate is: the bigger the margin of error, the less certain the estimate. In general, estimates from the ACS have larger margins of error than estimates from the decennial census long form because of the lower sampling rates in the ACS.

The Census Bureau lists margins of error alongside the ACS estimates. These published ACS margin of errors are for the 90 percent confidence interval, meaning we can be 90 percent confident that the true number falls somewhere within the range or “confidence interval,” described by the published estimate plus or minus the margin of error.

Most of the time it’s very important for you to include the margins of errors when using ACS estimates because margins of errors can be particularly high for small population groups and for small geographic areas.

If a margin of error is too high for a suitable level of accuracy, you may need to:

Collapse data categories
Look at broader geographies
Choose a different estimate series to increase the sample size

If you need to derive new margins of errors because the desired answer combines geographies or data categories, this requires a formula that involves more than just adding up the margins of errors of the estimates. The following are two good resources for understanding more about combining margins of errors:

Statistical formulas provided in the Census Bureau’s documentation on the ACS, including in the Compass Series handbook. (See pages 10‐11 and appendices 3 and 4.)
Handy and time saving statistical calculators have also been developed by organizations, like the New York State Data Center's statistical tool.

Comparing ACS Data

The strength of the American Community Survey is in estimating characteristic distributions. The U.S. Census Bureau recommends users compare derived measures such as percents, means, medians, and rates rather than estimates of population totals.

Whether you are comparing ACS data across different time periods or against the decennial census, it is important to be aware of the differences in methodology, time periods, and geographies.

When comparing ACS data for different time periods:

Always use the same estimate series (1-year with 1-year, 3-year with 3-year)
Try to use non-overlapping periods (for example, compare a 2005-2007 ACS 3-year estimate to a 2008-2010 ACS 3-year estimate)
Be aware of geographic changes. Estimate series prior to 2010 use the 2000 census geography which can be different from the geographies used by the 2010 and later estimate series. See Geographic Files and Maps Data Issues for more information.

When comparing ACS data to the decennial census be aware of:

Differences in the universe of the population being sampled
Question wording
Residence rules
Reference periods
The way in which the data are tabulated

The U.S. Census Bureau provides guidance on all these issues including an easy table comparison tool.

Additional Help on Using the ACS

For more information about comparing ACS with decennial census data, margins of error, or estimate series differences, consult the following:

Puget Sound Regional Council User’s Guide to the American Community Survey
U.S. Census Bureau Compass Products

Additional Data Resources

Additional information about the ACS is available from:

1-Year Data Series

What Does Seattle Look Like?

3-Year Data Series

What Does Seattle Look Like?

5-Year Data Series

What Does Seattle Look Like?

Data Issues

Know Your Estimate Series

Population Control Totals

Margins of Error

Comparing ACS Data

Additional Help on Using the ACS

Additional Data Resources

Planning and Community Development

City-Wide Information

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