Migration Begets Migration

Lyman Stone
In a State of Migration
6 min readAug 25, 2015

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New ACS Data With Migration by Place of Birth Shows Importance of Personal Ties

It’s apparently data release season for migration researchers. Today, the Census Bureau released new County-to-County migration flows data from the American Community Survey. This is great data as it allows us to test and corroborate IRS bilateral flows data, and gives us some unique crossing variables that the IRS data doesn’t have. For each new sample, the team at ACS chooses a different set of variables to cross the data, usually along some kind of theme. For this most recent sample, reflecting the period 2009–2013, they apparently decided to make their theme “fun variables that directly relate to historic migration.” We can cross ACS 2009–2013 migration flows data by place of birth, year of entry into the US, and English language proficiency. For immigration researchers, this is a goldmine. But even for domestic migration researchers, this is very interesting stuff. Eventually, I’ll have to update my posts on how international and domestic migration relate. But for today, I’m just going to offer a quick sample of the kinds of questions the new ACS data can help us answer.

To explore the data, I will look at some summary information about migration in Kentucky based on place of birth.

Migration and Place of Birth

Birth Groups and Flow Shares

The above chart shows each major “birth group” (Kentucky-born, other-US, and foreign-born) and, for each group, has a bar for that group’s share of a given migration flow: international inflows, domestic inflows, domestic outflows, and flows within Kentucky. The resulting shares are fairly predictable at face value. Kentucky-born individuals dominate migration within Kentucky, the foreign-born dominate migration from abroad, and non-KY US-born dominate flows to and from the rest of the US. This is just population gravity at work. There are more foreigners abroad than there are Kentuckians, so of course Kentuckians have a lower share. Notably, however, fully 15% of all inflows from abroad are still of Kentucky-born individuals. When you think about it, that’s kind of remarkable.

About 1 in 6 “immigrants” into Kentucky is Kentuckian by birth.

Another 1 in 4 immigrants was born somewhere else in the US. In other words, while the largest share of international inflows is indeed the foreign-born, foreign-born people (including Americans born abroad to American citizen parents) make up only 57% of all international inflows. If I could include breakout the diasporan-born and those from US territories, there’s a good chance that non-Americans make up less than half of all immigration into Kentucky. So keep in mind that “international migrants” are often actually “from around here.” We live in a mobile world.

Migration and Place of Birth

Birth Groups and Gross Rates

The above chart, instead of showing shares, shows rates. So the pale green tall bar for the Kentucky-born indicates that 3.5% of the Kentucky-born within Kentucky migrated within the state per year from 2009–2013. The short, dark green line for Other US-Born shows that about 0.3% of those born around the US outside of Kentucky migrated from abroad per year from 2009–2013. And so on.

The different birth-groups have radically different migration rates for some forms of migration, and similar for others. For example, all groups had about the same rate of migration within Kentucky. The Kentucky-born were the highest at 3.5% and the foreign-born the lowest at 3.3%, but these are not significant differences. On the whole, we can say that local migration practices are similar across origin groups. The same is not true for other forms of migration.

Interstate migration is 7 times higher for non-Kentuckians residing in Kentucky than for Kentuckians.

Less than 1% of Kentucky-born people living in Kentucky will migrate into or out of the state in a given year. Meanwhile, about 5% of the non-Kentuckians will migrate into or out of the state. This makes sense (Kentuckians living in other states have similar rates) but may take some explaining.

Essentially, there’s a selection bias. Kentucky-born people living in Kentucky, in most cases decades after birth, likely have most of their social and professional ties within the state. This is a population self-selected to have a low likelihood of migration because they’re a group that has chosen to live near their birthplace. So of course they have a low migration rate!

Meanwhile, the migration rate for other US-born people has a similarly simple explanation. A person born elsewhere and living in Kentucky is by definition already a migrant. They have ties in multiple places of some kind, and may have a more geographically diverse network. Many may just be college students who expect to return home, or go on somewhere else entirely. Once people start moving around, they forge networks and connections that facilitate further migration in the future, and develop habits and a lifestyle that incorporate migration.

Migration begets more migration.

This shows up with the foreign-born as well. They have higher domestic migration, despite lacking the possible birth tie somewhere else of the non-Kentucky US born. But they are migrants nonetheless, likely to have a lower inhibition to leaving, less rooted to the local area.

Migration and Place of Birth

Conclusion

There’s a lot more that can be done with this data, and I hope to show some of that in future posts. But for now, it’s enough that this data shows us a few simple if important truths about migration. First, migration rates vary widely between people who have opted for a more “sedentary” lifestyle and those who have chosen a more “migratory” lifestyle. Those who stay close to their place of birth are less likely to migrate — ever. Those who move are more likely to move again. This shows that future migration is in some sense conditional on previous migration. In other words, migration begets more migration.

See my last post showing how new IRS data elucidates questions of age and income in migration.

Start my series on migration from the beginning.

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I’m a graduate of the George Washington University’s Elliott School with an MA in International Trade and Investment Policy, and an economist at USDA’s Foreign Agricultural Service. I like to learn about migration, the cotton industry, airplanes, trade policy, space, Africa, and faith.

My posts are not endorsed by and do not in any way represent the opinions of the United States government or any branch, department, agency, or division of it. My writing represents exclusively my own opinions. I did not receive any financial support or remuneration from any party for this research. More’s the pity.

Cover photo source.

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Lyman Stone
In a State of Migration

Global cotton economist. Migration blogger. Proud Kentuckian. Advisor at Demographic Intelligence. Senior Contributor at The Federalist.