# Pooling ACS and Census extracts

**URL:** <https://forum.ipums.org/t/pooling-acs-and-census-extracts/3715>\
**Category:** USA\
**Created:** [August 28, 2020, 7:17pm UTC](https://forum.ipums.org/t/pooling-acs-and-census-extracts/3715 "2020-08-28T19:17:03Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![jdikatz](https://avatars.discourse-cdn.com/v4/letter/j/df705f/32.png) [@jdikatz](https://forum.ipums.org/u/jdikatz)\
**Post date:** [August 28, 2020, 7:17pm UTC](https://forum.ipums.org/t/pooling-acs-and-census-extracts/3715/1 "2020-08-28T19:17:03Z")

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I’m considering pooling some of the ACS and Census samples – in particular, the 2000 ACS with the 2000 5% Census sample, and the 2010 ACS with the 2010 10% Census sample.

Are these samples non-overlapping? If so, I do not think I would want to pool, as some people might be double-counted. If not, I think I would want to adjust the weights in each sample so that the weighted count sums up to the total population count – specifically, I would multiply each weight in each sample by the ratio between the unweighted count in that sample and the unweighted total count across all samples in a given year.

Lastly, are the Census extracts broadly comparable to the ACS in surrounding years? For instance, can I compare the 2009 ACS to the 2010 Census extract?

Are there other issues I’m not considering?

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**Author:** ![KariWilliams](https://avatars.discourse-cdn.com/v4/letter/k/82dd89/32.png) [@KariWilliams](https://forum.ipums.org/u/KariWilliams)\
**Post date:** [September 1, 2020, 5:40pm UTC](https://forum.ipums.org/t/pooling-acs-and-census-extracts/3715/2 "2020-09-01T17:40:20Z")

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Unless you have a distinct need to pool the samples, I don’t recommend doing this because (for most use cases) there isn’t much benefit.

The detailed topical coverage in ACS data is not available in the 2010 decennial (ACS fully replaced long-form decennial by 2010); while both the long-form and ACS were fielded in 2000, ACS was in beta and the sample size is pretty small (both in comparison to the decennial PUMS and subsequent years of ACS). I cannot definitively say that augmenting the number of unweighted cases for short-form questions by including ACS wouldn’t make a difference, but will note that the decennial sample sizes are quite large (1-in-20 for 2000 and 1-in-10 for 2010).

I cannot find any documentation that indicates these samples are non-overlapping (I think they are drawn independently and, therefore, assume that they do overlap given the large sample sizes for decennial PUMS). Here is additional information on the [2000 decennial sample design](https://usa.ipums.org/usa/voliii/2000samp.shtml), the [2010 decennial sample design](https://usa.ipums.org/usa/voliii/2010samp.shtml), and the [ACS sample design](https://usa.ipums.org/usa/voliii/ACSsamp.shtml).

However, if you are interested in pooling ACS and decennial data, there are a few things to keep in mind (hopefully this addresses your question about broad comparability):

- The reference period varies: point-in-time (decennial) versus rolling data collection (ACS–noting that the public use data do not note the month of data collection)
- Residence requirements: usual residence (decennial) versus current (ACS)
- Pay close attention to the universe and question phrasing as they may differ slightly between the ACS and the census (most notably in 2000 when both the long-form decennial and ACS were fielded).

I also recommend reviewing this [summary of differences between the ACS and decennial census](https://www.census.gov/content/dam/Census/library/publications/2018/acs/acs_general_handbook_2018_ch09.pdf) and this [FAQ about comparing ACS data](https://www.census.gov/programs-surveys/acs/guidance/comparing-acs-data.html).