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Net Migration and Population Estimates: A High-Level Overview

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The U.S. Census Bureau recently released population estimates to help us gauge change in the population since the 2010 Census. Births, deaths and net migration are the main components of population change. Net migration is the difference between the number of people moving into an area and the number of people moving out. The net migration component is comprised of both domestic migration (moves where both the origin and destination are within the United States, excluding Puerto Rico) and international migration (any change of residence across the borders of the United States). Change in net migration typically causes most of the changes in population trends because migration is more likely to experience short-term fluctuations than births and deaths.

The Census Bureau bases its estimate of county-level net domestic migration on three administrative records data sources: Internal Revenue Service tax exemptions, change in Medicare enrollment, and change in the group quarters population (e.g., college dormitories, prisons, and nursing homes).

Let’s take a closer look at some considerations when using the IRS tax exemptions data and how we calculate and apply the migration rates for ages 65 and under. In this context, an IRS exemption refers to an individual that appears on a tax return, either as the primary filer, a spouse, or as a dependent. Not all residents are represented in the tax exemption data because not everyone files taxes. Therefore, IRS-based "exemptions" are not equivalent to "migrants." We estimate migrants by applying IRS-based net domestic migration rates to the mid-year household population. These rates are calculated in two steps. First, IRS-based net migrant exemptions are computed by subtracting the number of out-migrant exemptions from the in-migrant exemptions for each county. Then, we divide the number of IRS-based net migrant exemptions by the population at risk to move that constitutes the total number of non-migrant exemptions and out-migrant exemptions for each county. These net rates are calculated separately for two age groups: under age 18 and ages 18 to 64.

The international migration component is primarily based on information from the American Community Survey (ACS). We create the national net international migration estimates through these general components: foreign-born immigration, foreign-born emigration, net Puerto Rico-U.S. migration, and net native-born migration. Foreign-born emigration is estimated by calculating emigration rates for certain populations based on country of birth, sex, and tenure in the U.S using the year of entry question.

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.


Page Last Revised - October 8, 2021
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