How Many Would Really Come if the Borders Were Open?

Analysis of a recent Gallup poll

By Matthew Sussis on May 8, 2019

A recent global Gallup poll found that 158 million adults around the world said they would migrate to the United States if they could. However, Gallup only polled adults, meaning the actual total number of people who would come to the United States is much larger because it would likely include children. Curiously, nowhere in the Gallup report are child family members mentioned. When one factors in a chain-migration multiplier, the number of potential migrants is much larger.

There are obviously a range of variables when it comes to guessing the full impact of the hypothetical migration of 158 million adults to the United States. Nonetheless, under different scenarios modeled below, we estimate that anywhere from 386 to 703 million people around the globe (adults plus children) would migrate to the United States if they could.

Of course, as Gallup notes, the number of actual migrants tends to be much smaller than the number of potential migrants. Still, these eye-opening numbers highlight the risks of an open-borders scenario, where anyone who'd like to come to the United States with their family has that option.

Scenario 1: Regional Fertility Rates

In our first scenario, we consider the fact that Gallup does not clarify which countries these 158 million adults come from, but it does tell us the total proportion of adults seeking to move to anywhere — not the United States specifically — by region. For example, 33 percent of Sub-Saharan African adults say they would leave Sub-Saharan Africa if they could; 27 percent of Latin American and Caribbean adults feel the same way.

As such, certain regions — Africa, Latin America, and the Middle East — are heavily overrepresented among potential migrants. Currently, most migrants to the United States come from Latin America and Asia, meaning in a true "open borders" scenario the migrant flow would shift more toward Africa and the Middle East where a higher proportion of people want to leave. Sub-Saharan Africans account for 14 percent of the global population, but 29 percent of total potential migrants.


Table 1. Potential Migration to the United States
Given Regional Fertility Trends and Open Borders


Region Pct. of Adults Seeking to Move Total Population (millions) Pct. of Global Population Number of Potential Migrants (millions) Pct. of Total Potential Migrants No. of Potential Adult Migrants to U.S. (millions) Fertility (children per woman) Total Potential Immigration Including Children (millions)*
Sub-Saharan Africa 33% 1,078.0 13.9% 355.8 29.1% 46.0 4.7 154.2
Latin America and Caribbean 27% 658.3 8.5% 177.8 14.6% 23.0 2.2 48.3
Europe (non-European Union) 26% 230.5 3.0% 59.9 4.9% 7.8 1.5 13.6
Middle East & North Africa 24% 418.0 5.4% 100.3 8.2% 13.0 3.1 33.1
European Union 21% 512.6 6.6% 107.6 8.8% 13.9 1.6 25.1
Ex-Soviet Commonwealth 15% 239.8 3.1% 36.0 2.9% 4.7 1.6 8.4
Northern America 14% 366.5 4.7% 51.3 4.2% 6.6 1.9 12.9
Wider Oceania 9% 38.8 0.5% 3.5 0.3% 452.1 2.4 1.0
East Asia 8%

1,658.2

21.4% 132.7 10.9% 17.2 1.6 30.9
South Asia 8% 1,891.0 24.5% 151.3 12.4% 19.6 2.6 45.0
Southeast Asia 7% 641.8 8.3% 44.9 3.7% 5.8 2.5 13.1
World 16% 7,733.7 100.0% 1,221.1 100.0% 158.0   385.6

Sources: UN Household Size and Composition Around the World 2017, Gallup global migration poll, Worldometers global population by region, 2019, UN World Fertility Patterns, 2015.
* Assumes women represent half of the population.

By applying those proportions to the 158 million adults who want to move to the United States, we can estimate the total number of potential migrants by region. For example, in this scenario we estimate that 23 million of those 158 million people would come from Latin America.

However, with regard to children, different parts of the world have different family sizes and different total fertility rates (i.e., the number of children likely to be born to a woman from that country over the course of her child-bearing years at current birth rates). Women in Sub-Saharan Africa have an average fertility rate of 4.7, whereas in East Asia that figure is just 1.6. Scenario 1 uses regional fertility rates to estimate the ratio of children to adults for each adult migrant coming to the United States.

This is an imperfect measure because it is likely that fertility rates will decline once a migrant moves to the United States. Nonetheless, our analysis includes a mix of potential future parents as well as current parents and the fertility rate remains a more precise variable than family size, which in many regions does not easily account for the proportion of dual vs. single parent homes.

Under this scenario, we estimate that 158 million adults moving to the United States would bring 227.6 million children with them, for a total migration wave of 385.6 million people.

Scenario 2: Chain Migration Multiplier

Rather than attempt to guess what the regional flows of these 158 million adults could look like, we can also consult existing academic studies for the family behavior of migrants already in the United States.

According to the most complete recent studies on chain migration, in recent years each new immigrant sponsored an average of 3.45 additional immigrants. In the 1980s, that multiplier was 2.59, or more than 30 percent lower.

In a hypothetical scenario where 158 million adults move to the United States in a short period of time, it's quite likely that the multiplier would rise even more, given that people are more likely to immigrate if they know someone else who has immigrated, and given that the multiplier has risen over time.

On the other hand, there is obviously some degree of family overlap among the 158 million adults — such as two brothers who would both come to the United States, or a husband and a wife.

Given these confounding variables in both directions, it seems most fair to simply apply the existing 3.45 multiplier to the 158 million people. Doing so would lead to an additional 545.1 million migrants, for a total migration of 703.1 million people.