ACS and COVID-19: Guidance for Using the PUMS with Experimental Weights
Due to the effects of the COVID-19 pandemic on 2020 ACS data collection and data quality, the Census Bureau has made several adjustments to the data products that contain 2020 data. They did not release their standard data products for the 2020 ACS 1-year data, including the standard Public Use Microdata Sample (PUMS). Instead, they released the 2020 ACS 1-year data products with experimental entropy-balance weights designed to account for the impact of the COVID-19 pandemic on the data quality. For the 2020 ACS 5-year data, the Census Bureau revised its methodology for weighting households by using their standard weighting methodology for the 2016-2019 portion of the data and the entropy-balance weighting methodology for the 2020 portion of the data. The experimental weights were also made available for the 2019 ACS 1-year data. Users can apply both standard weights (HHWT and PERWT) and experimental weights (EXPWTH and EXPWTP) to analyses utilizing the 2019 ACS 1-year PUMS file.
IPUMS USA continues to harmonize the ACS single- and mutli-year PUMS files that contain 2020 data on the IPUMS USA website, however, the Census Bureau encourages users to proceed with caution when using samples that contain 2020 data.
This page provides a brief overview of the impacts of the COVID-19 pandemic on data collection and resulting data quality, the development of the experimental entropy-balance weights, and guidelines for using the ACS PUMS files that contain 2020 data. See the reference list included on this page for links to additional documentation providing greater detail about the 2020 ACS 1-year data products, the experimental entropy-balance weights, and other ACS PUMS samples that contain 2020 data. The information below applies to samples including the 2020 ACS sample (e.g. 2017-2021 ACS 5-year sample)
|TABLE OF CONTENTS|
|Impact of the COVID-19 Pandemic on Data Collection and Data Quality|
|Development of the Experimental Weights|
|Guidelines for How and When to Use the ACS PUMS Files that Contain 2020 Data and the Experimental Weights|
Impact of the COVID-19 Pandemic on Data Collection and Data Quality
The COVID-19 pandemic significantly disrupted ACS data collection strategies, affecting the 2020 ACS 1-year PUMS file. Data collection typically occurs using two strategies: the mailout strategy and the computer-assisted personal interviewing (CAPI) strategy).
The mailout strategy includes five phases: an initial mailing, a reminder letter, a questionnaire package, a reminder postcard, and a final reminder. Each of these phases were affected at different times and to different degrees from March 2020 through the end of the year, resulting in large impacts on the ACS response rate. The CAPI operation strategy was also affected, such that field operations were suspended or reduced for a majority of the 2020 data collection year. Data collection for group quarters was especially disrupted by the COVID-19 pandemic; in-person visits to group quarter facilities were suspended or greatly reduced from March 2020 through the end of the year, and telephone interviews were not conducted due to logistical constraints. For a more detailed description and timeline of how these data collection strategies were impacted, see section two of the working paper: An assessment of the COVID-19 pandemic's impact on the 2020 ACS 1-year data. The 2020 ACS had significant variability in response rates for both housing units and group quarters across the 2020 data collection year, and had the lowest overall response rate in the history of the ACS.
Due to data collection disruptions and resulting data quality issues, the Census Bureau determined that the resulting sample did not meet their data quality standards, and they would need to take additional measures to adjust for the impacts of the pandemic on the 2020 data file. Data quality issues they found included:
Variables related to socioeconomic status, building structure, marital status, educational attainment, Medicaid coverage, citizenship, income, and poverty were particularly affected. These data quality issues resulted in biased estimates, especially for historically underrepresented populations.
Development of the Experimental Weights
To address the impacts of the COVID-19 pandemic on data collection and resulting data quality, the Census Bureau developed and applied additional weighting methodology to the 2020 ACS 1-year file; the resulting weights are referred to as the experimental weights in the Census Bureau and IPUMS documentation. Broadly, the changes to the weighting process addressed the following components:
Adjusting for the high level of non-response bias was one of the most important aspects of developing the experimental weights. To address the non-response bias, the Census Bureau drew from administrative, third-party, and decennial census data to develop entropy balance weights using methodology tested on the Annual Social and Economic Supplement (ASEC) of the Current Population Survey (CPS). Once developed, the entropy balance weights were first tested against standard benchmarks, such as the distribution of income and earnings, and were found to successfully reduce the non-response bias in the 2020 sample. The entropy balance weights were then applied to the 2019 ACS 1-year file for evaluation on a more standard ACS data sample. The large changes between 2019 and 2020 that were observed prior to applying these weights reduced to normal levels, suggesting that the entropy balance weights were reducing the abnormal effects of the pandemic on the 2020 ACS 1-year data file without changing the normal level of expected change. For more information about the development and assessment of the entropy balance weights, see the working paper, Addressing nonresponse bias in the American Community Survey during the pandemic using administrative data.
The U.S. Census released experimental weights for the 2019 ACS 1-Year file to allow users to utilize both standard weights and experimental weights in their analyses. These weights are available for both the 2019 1-Year ACS and 2020 1-Year ACS under the variable names EXPWTH and EXPWTP.
Overall, the experimental weights developed for the 2020 ACS 1-year data products address the known data quality issues, especially issues resulting from the high level of non-response during the 2020 data collection year. Users should still proceed with caution when using the 2020 ACS 1-year data products. The next section provides guidelines for using the 2020 ACS 1-year PUMS file and experimental weights.
Guidelines for How and When to Use ACS PUMS Files that Contain 2020 Data and the Experimental Weights
Considerations for using the 2020 ACS 1-year PUMS file:
Considerations for using other ACS PUMS files that contain 2020 data:
Considerations for using the PUMS experimental entropy-balance weights: