2020 and combining samples

I’m updating a project where in the past I used three 1-yr ACS samples. Do you have thoughts on the pros and cons of using 2019, 2021, and 2022 vs 2021 and 2022? Obviously, the two-year sample will be smaller, but it won’t have any pre-pandemic data.

Thanks for any insights.


There are several factors to take into account when using 2020 ACS data (see this user note on using samples with 2020 ACS data); the Census Bureau encourages users to proceed with caution when comparing data products containing 2020 data with other years. However, this was no particular guidance issued for comparing pre-2020 with post-2020 samples. The issues with response rates that the ACS encountered in 2020 were not significant enough in 2021 to warrant experimental weights or any specific note to caution users not to compare the data with other years. Therefore, whether you want to use pre-2020 samples in your project will depend more on your research question and methodology.


Thanks for your response. I’m interested in some pre-pandemic and post-pandemic—or post-2020—comparisons. So I’ve decided to compare 2018-19 and 2021-22 2-yr estimates. Any words of advice or caution?



Nothing specific comes to mind regarding comparing estimates from these two samples. A general note is that you will need to use weights (PERWT and/or HHWT) to make your estimates using the ACS samples nationally representative. See this FAQ on weights for more information.