Every year, the U.S. Census Bureau releases an updated series of its official population estimates. Relying on the 2010 Census counts as a starting point, estimates at the national, state, county, and subcounty (cities and towns) levels are developed using current data on births, deaths, and migration (also known as the components of population change.) The result is a set of estimates referred to as a “vintage,” where the term vintage denotes estimates created with a consistent population starting point and methodology. Each vintage features estimates for April 1 of the latest census year to July 1 of the current, or vintage, year. The release of a new vintage supersedes any previous estimates series because the new series incorporates the most up-to-date data and methodological improvements. Differences between estimates from one vintage to the next (e.g., July 1, 2015, estimates from Vintage 2015 as compared to July 1, 2015, estimates from Vintage 2016) are usually due to data updates, changes in methodology, or legal boundary changes where places or counties add or lose land area.

A previous blog explored the role of migration as a major driver of population change. With regard to this component, the Vintage 2016 population estimates reflect two notable changes to the migration methodology relative to last year’s (Vintage 2015) published estimates:

• Domestic Migration:

In Vintage 2016, we changed how we handle duplicate tax records belonging to children under 18 years of age. Two tax records can exist for the same person when an individual files a return and is also claimed as a dependent on someone else's return. For the Vintage 2016 time series, we preserved the tax record where children appear as dependents instead of choosing the tax return designating them as a filer. Prior to Vintage 2016, we always selected the tax record that an individual filed on his/her own behalf (regardless of age). This change in record selection is more consistent with Census Bureau residence rules, as we typically expect dependent children under the age of 18 to live in the same household as their parents or caretakers. Following this change, the vast majority of counties showed little to no difference. However, because of this methodological change, the age distributions of in- and out-migrant exemptions improved throughout the time series.

• Net International Migration:

Emigration is the act of leaving one’s resident country with the intent to settle in another. These rates were applied to nine mutually exclusive populations at risk of emigrating, which produces an annual emigration estimate: (1) Recent Mexican Males, (2) Recent Mexican Females, (3) Non-Recent Mexicans, (4) Latin Americans, (5) Recent Canadians/Europeans, (6) Non-Recent Canadians/Europeans, (7) Recent Asians, (8) Non-Recent Asians, and (9) Other. For the purposes of our net international migration estimate, we estimate both foreign-born and native-born emigration.

For the 2016 population estimates release, the foreign-born emigration subcomponent was updated in two ways:

(1) The emigrant group definitions used to calculate estimates of foreign-born emigration were modified. We redefined the groups based primarily on recent/non-recent status. We retained the current Mexican emigrant groups (recent/non-recent and male/female) and recent Canada/Europe and recent Asia groups. We reintroduced the Recent All Other Countries and Non-Recent All Other Countries. This proposed change will reduce the number of groups from nine to seven.

(2) We use a fixed rate derived from the average of rates for all available five-year American Community Survey (ACS) data. The fixed rates were used for non-recent arrivals including Non-Recent Mexico, Latin America, and Non-Recent Asia groups for the entire time series. These changes resolve negative rates produced by the previous residual method, which had resulted in demographically implausible rates such as zero emigration for certain emigrant groups. Consequently, foreign-born emigration will be higher and net international migration is lower than it was for the previous vintage.

However, the overall impact attributed to these changes on the Vintage 2016 county totals is minimal. Even so, these methodological improvements position our processes for the 2020 Estimates Evaluation as we continue to develop these estimates into the future.

The U.S. Census Bureau’s Population Estimates Program produces and publishes estimates of the resident population for the United States, its states, counties/county equivalents, cities and towns collectively known as “subcounty” areas, as well as for the Commonwealth of Puerto Rico and its municipios. The resident population includes all people currently residing in the United States. These estimates are used to allocate federal and state funds, as well as serving for controls for major surveys, government data collections, and public and private research.

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