How did IPUMS determine which SMSAs to disclose for 1970 USA samples?

USA
1

I am working on a project to compare the codistribution of earnings and home prices between large and small metropolitan areas from 1970 to 1990.

I have a question about how IPUMS deals with changing MSA/SMSA definitions.

The documentation here states that in 1970, SMSAs are only identified if their population is greater than 250,000.

In the 1970 sample I downloaded, Brockton, MA is identified.

I have struggled to find a list of 1970 SMSA populations. I ended up transcribing populations by hand from pages 1-171 to 1-178 of the attached document, which was downloaded from the census. According to this document, the population of the Brockton SMSA in 1970 was 189,820.

this is well under the stated threshold, so why is Brockton, MA disclosed in the sample?

If anyone could provide a list of the SMSA populations that IPUMS used in choosing which SMSAs to disclose and not to disclose, this would be greatly appreciated.

1970a_us1-05-1.pdf (9.47 MB)
1970a_us1-05.pdf (9.47 MB)

2

This is a good question. A couple of details might be helpful. First, according to the 1970 metropolitan sample, there are 329,600 people living in the Brockton, MA metropolitan area. Second, it looks like in the census document you are referencing only parts of counties are included in the Brockton MSA. I’m not sure what method the census is using to break apart counties, but in the IPUMS sample entire counties are included in MSAs. More specifically, in the 1970 metro samples, entire “county groups” (i.e. combinations of counties totaling at least 250,000 people) are included in MSAs. So, the Brockton MSA is comprised of the entire Plymouth, MA “county group”.

I hope this helps.