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Status:Closed    Asked:Sep 03, 2018 - 06:46 AM

why pwmetro metarea categories different?

Dear forum,


According to US census bureau, there are 280 MSA categories in the year 2000 (https://www.census.gov/population/cen...),but in IPUMS-USA I noticed that there are about 380 MSAs for the variable "pwmetro" (between 2005-2011) and the categories of MSAs for "metarea" is also different. I am wondering why these MSAs are inconsistent? How can I map the "pwmetro", metarea" and census bureau MSAs ?


Many thanks.

 
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Staff Answer

Responding to: "I am trying to figure out the county composition of pwmetro, can I use the compositin file for "metarea"(https://usa.ipums.org/usa/volii/count...)?"


In short: yes and no.


The composition tables you linked to accurately describe the metro areas on which both METAREA and PWMETRO are based. I.e., we use the same metro area definitions as the basis for both METAREA and PWMETRO.


However, neither METAREA nor PWMETRO can exactly identify the populations (or worker populations) of the specific set of counties comprising every metro area. Census PUMS files don't identify counties or metro areas; they identify only PUMAs (and place-of-work PUMAs), which sometimes straddle multiple counties. As noted in the PWMETRO variable description: "PWMETRO identifies the metropolitan area in which the respondent worked, if the respondent's workplace was in an identifiable metropolitan area, given confidentiality restrictions," and METAREA uses a similar protocol. This means that any persons who lived in a PUMA, or worked in a PWPUMA, that straddled a metro area boundary are assigned "Not identifiable" codes in METAREA or PWMETRO, respectively.


This page identifies the portions of each metro area's population that are coded as "Not identifiable" in the METAREA variable. Because place-of-work PUMAs are occasionally larger than PUMAs, and may straddle metro area boundaries even where PUMAs do not, PWMETRO will have higher rates of unidentified populations for some metro areas. Unfortunately, however, we do not at this time have any summary information available on the unidentified populations for PWMETRO. In order to determine what portion of a metro area is not identified by PWMETRO, you'd have to use the metro area county composition info in conjunction with PUMA and PWPUMA composition info. If you have any familiarity with GIS or mapping software, you may also use boundary files from IPUMS USA and IPUMS NHGIS to determine how PWPUMAs correspond to metro areas.


The complexity of this problem is why we took a different approach for the MET2013 variable, and will be taking a different approach in a new version of PWMETRO ("PWMET13") for 2000 and ACS samples that we plan to release later this fall. For these new variables, we identify metro area codes only when PUMAs align reasonably well (within a 15% population tolerance) with the metro area, and we provide more complete composition information, as previewed in my answer to your other User Forum question.


 

Sep 10, 2018 - 09:25 AM

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Counting only the MSA's with an "X" in the PWMETRO code list, I see that the IPUMS-USA 2011 ACS sample identifies 293 MSA's. I get a number closer to 380 (363) only if I also count the codes that are not identified in 2011 (the N/A code plus all codes marked with a "."). Are you perhaps counting all of these cases? Most of the codes that are not identified om 2011 (those marked with a ".") are MSA's that were identified only in older census years (1990 and 1980).


You'll note that there is still a difference between the 293 codes identified in the 2011 ACS sample and the 280 codes in the ranking table you linked to. That's because the ranking table lists "consolidated MSAs" (CMSAs), which consist of two or more "primary MSAs" (PMSAs), and IPUMS USA codes identify the component PMSAs separately. E.g., the ranking table identifies "Dallas--Fort Worth, TX CMSA" as a single entity, but PWMETRO codes separately identify "Dallas-Fort Worth, TX" (code 1920) and "Fort Worth-Arlington, TX" (code 1921).


(Note that the IPUMS USA labeling of metro areas can be misleading. In the 2011 sample, PWMETRO code 1920 does _not_ include Fort Worth. Only code 1921 does. For more info, see the discussion of "The METAREA Label System" in the METAREA variable description. We hope to improve this labeling in the future.)


The codes for the METAREA and PWMETRO variables should all align with each other correctly (i.e., a single metro area will have the same code in both variables), but we are able to identify a somewhat larger set of codes for METAREA than for PWMETRO. That's because IPUMS USA determines METAREA (the metro area of residence) based on Public Use Microdata Areas (PUMAs) and determines PWMETRO (the place-of-work metro area) based on Place-of-Work PUMAs (PWPUMA00). Some Place-of-Work PUMAs are larger than standard PUMAs, and they may straddle metro area boundaries in different ways, so it is not possible to identify as many place-of-work metro areas as metro areas of residence.


To understand the relationships between IPUMS USA codes and the original Census/OMB codes, see the discussion of "The METAREA Code System" in the METAREA variable description. In general, each IPUMS USA code corresponds directly to a single MSA or PMSA in Census sources, but the codes may differ.


 

Sep 04, 2018 - 04:14 PM

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Thank you for your clarification! Since pwmetro and metarea are constructed from differnet variables, does the same MSA code in pwmetro and metarea have different boundaries? I am trying to figure out the county composition of pwmetro, can I use the compositin file for "metarea"(https://usa.ipums.org/usa/volii/count...)? Thanks again !

 

Sep 10, 2018 - 12:47 AM

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