Status:Closed    Asked:Dec 03, 2015 - 09:54 AM

How many unique counties are in a 5-year, 3-year and 1-year ACS file?

The following link from ACS says that there should be 3,220 unique counties of any population size presented in a five-year survey. The 1-year only shows those counties with 65,000+ residents.

My file has each of the 5-year ACS files in it. My count of unique counties comes out at 423 (less if I ignore 0000 examples), which is much fewer than 3,220.

That is the same number of counties as when I use the ACS 1-year files. If I understand the ACS page correctly, there should only be 65,000+ counties in the 1-year file, while the 5-year file contains all counties no matter population. As a result the ACS 1-year should not have the same number of counties as the ACS 5-year.

Please help shed some light on this.

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Staff Answer




Your link describes the county data availability for published ACS estimates; therefore, it does not apply to the ACS microdata. In fact, the Census Bureau does not identify any counties in its public-use microdata. As a result, IPUMS must recover county information using PUMAs, which are areas with 100,000+ residents. Any county with fewer than 100,000 residents cannot be identified. As of the 2010 Census, fewer than 600 counties met this population threshold.

Among those with sufficient population, a county is only identifiable if it is coterminous with a single PUMA or if it contains multiple PUMAs, none of which extend into other counties. You can find a list of counties available on the County variable description page.

Hope this helps.


Dec 03, 2015 - 05:18 PM

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