Hello! I am currently using IPUMS ACS and ATUS for my analysis. My analytic time frame is 2005 to 2023. I’ve created metropolitan-level variables using ACS; I used the MET2013 variable. I want to link these metropolitan-level variables to ATUS. I am not sure whether to use METAREA or METFIPS. Based on my own exploratory analysis, the main difference between the two variables is that sample sizes tend to be smaller for smaller metropolitan areas and larger for bigger metropolitan areas when using METAREA comapred to METFIPS. Any suggestions will be appreciated. Thank you!
Combining ACS and ATUS metropolitan identifiers into a single analysis presents some comparability issues. As I explain below, my advice is to use IPUMS NHGIS to obtain metropolitan statistics from the ACS summary files (rather than from the IPUMS USA microdata). You can then link statistics to either the IPUMS ATUS variables METFIPS or METAREA depending on the areas that you want to analyze, with two important caveats: (a) estimates from smaller areas and especially those with with a total population of less than 500,000 should be treated with caution, and (b) changes to metropolitan delineations in the ACS summary data as well as in the ATUS will affect the comparability of your estimates across these vintages and across surveys.
While both the metropolitan statistical area (MSA) and the combined statistical area (CSA) of residence is directly reported for respondents in the IPUMS ATUS variables METFIPS and METAREA respectively, this is not the case for respondents in the ACS microdata. In these samples, only the state and the Public Use Microdata Area (PUMA) are provided. IPUMS geographers assign metropolitan identifiers in variables such as MET2013 and METAREA by overlaying PUMA boundaries with metropolitan boundaries and applying a population-based identification protocol. As a result, not all metropolitan areas can be uniquely or consistently identified in ACS microdata (see the MET2013 description tab for our protocol). If your goal is to use the ACS to produce metropolitan-level summary measures, then a better alternative is to use IPUMS NHGIS. This project integrates the Census Bureau’s 1-year and 5-year ACS summary files, tabulating variables for many different geographic levels. Note that NHGIS summary tables use metropolitan delineations that are contemporaneous with the survey year. This differs from MET2013, which applies consistent 2013 Office of Management and Budget (OMD) delineation across samples (see the 2013 CBSA delineation file on our geographic resources page).
Moving to your ATUS analysis, the decision of whether to use METFIPS or METAREA will depend on the number of areas that you would like to identify and the minimum precision that you set for your estimates. The MSAs reported in METFIPS are more detailed than the CSAs in METAREA since CSAs consist of combinations of metropolitan and/or micropolitan areas. This allows you to identify more areas, but with overall less precision due to smaller sample sizes. The Census Bureau provides the following cautionary note (applicable to the ATUS as a subsample of Current Population Survey respondents):
One set of estimates that can be produced from CPS microdata files should be treated with caution. These are estimates for individual metropolitan areas. Although estimates for the larger areas such as New York, Los Angeles, and so forth, should be fairly accurate and valid for a multitude of uses, estimates for the smaller metropolitan areas (those with populations under 500,000) should be used with caution because of the relatively large sampling variability associated with these estimates.
In addition, it is important to consider the issue of changing MSA and CSA boundaries both across years and the timing of these changes across the two surveys. The US Office of Management and Budget (OMB) updates MSA & CSA boundaries about once a decade. These revisions create new areas, demote others, and determine which counties are associated with an MSA/CSA (refer to the historical delineation files). The ATUS applies one set of boundaries from May 2004 through April 2014 (2003 delineations), and another beginning May 2014 (the same 2013 OMB delineations as in MET2013). Meanwhile, the ACS uses 2003 delineations in 2003-2012, 2013 delineations in 2013-2022, and 2023 delineations in 2023-onward samples. This not only affects comparability of estimates across vintages, but also requires matching vintages correctly between the ACS and ATUS (e.g., 2013 ACS data uses the 2013 delineations while the 2013 ATUS uses 2003 delineations).