In Part 1 we considered the official numbers for apprehensions at the Mexico-U.S. border and how the meaning of those numbers fluctuates over time. Now we’ll consider ways to estimate the number of unauthorized border crossers who become part of the general U.S. population—that is, the ones who either evade apprehension or are allowed to remain after apprehension.
For these numbers we need to
use estimates based on various sources. As with the apprehension numbers, the
metrics for the data in these sources aren’t necessarily consistent over time.
Adding to our difficulties, most government data uses the U.S. fiscal year,
which begins in October, while other sources may use the calendar year, or even
comparisons between certain months.
We will note these
discrepancies but won’t try to adjust for them. All estimates will be rounded
to the nearest thousand.
Calculating Changes in
the Undocumented Population
One way to estimate the
number of successful border crossers is to study changes in the size of the
undocumented population.
The traditional approach to
determining this population’s size is the residual method. Demographers start from the estimated number of immigrants in Census
Bureau’s annual American Community Survey (ACS), subtract the number of naturalized citizens
and green card holders, make adjustments for underreporting, and come up with
an estimate for the undocumented population in that year. (Note: the ACS is
based on the calendar year.)
Conservatives frequently claim
this method undercounts
the undocumented population, but it has proved itself in a real-life test: the “amnesty” of 1986. The number of migrants applying for
legalization was within the range the residual method predicted. Since then a
number of refinements have led to more detailed ACS-based estimates.
A further refinement of the
residual method is presented by demographers Robert Warren and John Robert
Warren in a 2013 paper.
In addition to estimating the size of the undocumented population from 1990 to
2009, they break out estimates for the number of unauthorized migrants that
entered the country each year and the number that left the count—by emigrating,
adjusting their status, being deported, or dying. The year of entry is provided
by the ACS, and DHS supplies the number of those who adjusted status or were
deported; mortality is based on standard mortality rates for Latino males based
on age.
The Warren and Warren estimates,
which run from 1990 through 2009, form a pattern not too far from that of
border apprehensions. The growth rate for the undocumented population reached a
high point in 2000 and then declined; by 2008 the number of people leaving the
undocumented population exceeded the number that entered.
 |
| Source: ProCon, based on Pew Research reports |
Two other studies show that
the decline continued for at least the next decade: a summary of
estimates through 2017 by Pew Research, and unpublished data supplied by the Center for Migration
Studies (CMS) extending the
Warren and Warren estimates to 2016.
But What About the
Overstays?
However, estimates of the
undocumented population don’t tell us how many of these migrants entered by
crossing the southwestern border. Many undocumented migrants enter with a visa
but overstay the visa’s expiration date; if they stay permanently, they become
part of the undocumented population.
In recent years this group may
have surpassed border crossers as a share of new undocumented arrivals.
The main source for an overstay
count is an annual “entry/exit overstay” report from DHS. The report for fiscal 2016 shows 50,437,278 entries by foreigners who
were issued visas for limited stays or were allowed to enter through the Visa Waiver Program. The department subtracts the number of visa holders
who adjusted their status—received new visas or applied for permanent
residence—and estimates the number of visa holders who exited the country
before their visas expired. The result is what DHS calls 739,478 “overstay events.” Subtracting people who simply
overstayed by a few months or less, DHS comes up with a 628,799 “suspected overstays.”
But these numbers are educated
guesses, as is shown by the term “suspected overstays.” The government has a
system for tracking people entering with visas, but tracking people leaving is
more difficult. Most enter and leave by air, along with some who travel by sea,
so it’s possible to track exits by consulting passenger manifests, but
matching the tens of millions of visa holders with the tens of millions of
manifests is a monumental task. And tracking is even more difficult for the
visa holders who enter and leave by land—mostly Canadians and Mexicans.
There are other hurdles to
estimating overstays. People who receive more than one visa in the course of a
year can overstay more than one time in a year, thus getting counted more than
once, and visa holders who die while in the US—elderly parents visiting their
children, for example—might be counted as overstays.
Correcting the Overcount
DHS’s estimate is a
significant overcount, according to demographer Robert Warren, who is Senior
Visiting Fellow at CMS. Warren uses the ACS data, including a breakdown by
national origin, to adjust the DHS overcount and provide a new estimate. Warren
and CMS Executive Director Donald explain the method in a 2018 article, and Warren describes the results in an accompanying article. The number Warren comes up with for 2016 is 306,000,
less than half the DHS number.
 |
| Source: Center for Migration Studies |
If we take this 2016 overstay estimate in conjunction with CMS’s 623,000 estimate for that year’s unauthorized arrivals, then these 306,000 overstays would account for 49 percent of the arrivals, while 317,000 migrants had presumably entered the U.S. population by crossing the border without authorization.
Warren gives somewhat
different figures in a 2019 CMS report, estimating arrivals at 515,000 arrivals and overstays at 320,000, or
62 percent. By this estimate, only 195,000 migrants—or 38 percent of total
arrivals—had entered the U.S. population in 2016 by crossing the border without
authorization.
Part 1: http://thepoliticsofimmigration.blogspot.com/2021/08/whats-relation-between-border.html
Part 3: http://thepoliticsofimmigration.blogspot.com/2021/08/whats-relation-between-border_26.html
Part 4: http://thepoliticsofimmigration.blogspot.com/2021/08/whats-relation-between-border_28.html
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