You could call it new insight gained over time. Or I can just say: I was wrong. Not just me. Most of the world’s migration experts were there too. 

A new academic paper debunks a highly influential theory which I’ve referenced frequently in my own articles: the concept of the "migration hump".

This seems like a good time to revisit that theory – and to consider the likely impact of this new research on migration policy, especially in Europe. Spoiler: the consequences look big. 

What is the migration hump? 

Let’s start with a quick look at the migration hump theory. Intuitively, you might think that as poor countries develop, fewer people will want to leave. But that’s not the case, or wasn’t, according to the theory. On the contrary: as a poor country develops, its progress will lead to increased outward migration from that country in the short term. Only when an economy achieves a certain level of income ( of $7,000 to $13,000, to be more precise), will emigration fall.

The reason: it costs money to emigrate, and many people in the poorest countries don’t have enough. As a country gets richer, the theory holds that more people will find the means to migrate. When or if that country becomes rich, reasons to leave will diminish steadily.

The theory dates back to although Dutch professor was the first to provide empirical evidence, in 2010. That evidence was based on fairly simple data: take a measure of the development of a country (either gross domestic product (GDP), or the then compare it to the rates of immigration and emigration. Compile a list of countries for comparison, and behold: the migration hump, a more or less hill-shaped curve, with the lowest rate of emigration in poor countries, the highest rates in middle-income countries, and falling rates for rich countries.

The migration hump has been a well-established concept since De Haas published his findings. It’s relied on by and policymakers. Everyone from the to the has been building on this work. 

Just last year Ton Dietz, former director of the Africa Study Centre in Leiden, took this as his theme at a conference of Dutch aid organisations: “Stop spreading the illusion that education and employment projects will lead to reduced migration,” he urged, “the opposite is true. More education, better health care, more employment, will all lead to more migration.”

The theory has also attracted serious attention from policymakers, as the European Union has pumped more and more money into migration policy – to discourage people from coming to Europe. 

Why do more migrants leave Mexico than leave Honduras? The reason could be that Mexicans are richer, or it may be just because they share a border with the United States

But if the migration hump was a valid assumption, the premise that increased spending on development aid will reduce net migration from poor countries is a misconception. If more development aid really did bring about more development, a country would rise up that "migration hump" curve – causing even more people to migrate. In other words, for low-income countries: more development = more emigration to Europe. 

I recently wrote on this very topic – armed with, concepts, the migration hump. My article that international aid can stop migration. I’ve referenced the theory in many other articles as well: in my story on for example, and in this conversation with

New research shows that I was oversimplifying. 

What’s changed?

Cue the new research More Development, Less Emigration to OECD Countries – Identifying Inconsistencies Between Cross-sectional and Time Series Estimates of the Migration Hump. If you don’t understand any of this, don’t worry. You’re not alone. 

Simply put, the structure of the paper follows two important steps. 

In step one, the researchers say: wait a minute. What the migration hump does is to show migration is more prevalent from middle-income countries than from low-income countries. But that doesn’t tell us anything about what happens when a country’s economy grows from low-income to middle-income. Isn’t it possible that there are other factors – apart from GDP or development – that play a role in causing people to migrate more often from middle-income countries? 

These other factors may explain why middle-income countries became richer than others in the first place. 

We can’t say that economic growth of X will lead to a shift in the emigration rate of Y. We can say that economic hump theory is wrong. – Claas Schneiderheinze

Take Mexico, for example. Mexico is richer than Honduras, and more people are migrating from Mexico to the US. Possibly (as the migration hump implied) this is because Mexicans are richer than Hondurans, and so can afford to migrate. But it may also be because Mexico shares a border with the US, so the trip is more accessible for Mexicans. This northern border may also explain why the Mexican economy is bigger than the Honduran economy: it’s easier to trade with a prosperous neighbour. Higher emigration may not be a factor of income at all, but a factor of Mexico’s geographical location.  

Shared borders are just one possible explanation. Another could be proximity to a Or whether a country has a coastline, making it accessible by sea. Or whether it has a very large population, or a very small one. Or if there is conflict in the country. As the researchers show, any and all of these factors affect not just economic development, but also the feasibility and attractiveness of migrating – to a richer country, or just to any country at all. 

Correlation or causality

Viewed from this perspective, it’s actually fairly odd that the migration hump is presented as a causal connection. Lower rates of migration from a particular poor country to, say, Europe, might be caused by differences in income – but they could just as easily reflect that the poor country is simply much farther away from Europe. We’ve established correlation, but

Step two of the study attempts to get a clearer answer to the issue of causality. To achieve that, you essentially have to move beyond comparing countries – that involves far too many other factors, which might explain more or less migration. Instead, you have to measure a country’s evolution: for example, how its economy changes over time. If Senegal gets richer, will migration go up or down? If Afghanistan becomes more developed, will the number of Afghans coming to Europe rise or fall? That’s what you want to know.

So that’s what the investigators looked at. They compared migration data for countries from 198 countries over a period of 35 years, to GDP data for those countries over the same period. What did they discover? When a country’s income rises, emigration to OECD countries goes down – even if the country is very poor to start with. In other words: there is no migration hump. 

Caveats and qualifications

To their radically disruptive findings, the researchers add some important caveats. “First of all,” Claas Schneiderheinze tells me by phone, “of course: this is still a correlation”.

Schneiderheinze co-authored the paper with David Benček, and is affiliated with the Mercator Dialogue on Migration and Asylum (MEDAM) research project. He explains: it’s possible that emigration decreases over time because income increases, but it’s also possible that both happen because of some other factor that was not measured. For example, because there is a new government. Or because oil prices went up. Or, because it rained more. In an ideal world, he tells me, “we would correct for every single factor that could potentially influence economic growth and migration”. But of course, that’s never possible. 

“Even so,” Schneiderheinze says, “this research comes closer to establishing causality than a comparison between countries. Now at least it’s about what really happened in one single country over time. Based on this data, we absolutely cannot predict that a 1% increase in GDP will lead to X% decrease in migration. But we can say that the migration hump is wrong.”

This brings me to the second caveat: the actual effect of changes in GDP is minimal. A tiny bit of economic growth doesn’t lead to a bigger, or even a proportionate, drop in migration. The research found that 1% growth in GDP reduces emigration on average by about 0.5%. Not exactly earth-shattering.

As the researchers themselves confirm, the primary significance of this data-crunching may be to tell us that any choice to migrate is far more complex than a calculation of income. 

Can development aid deter migration? 

When I read this paper for the first time, I was shocked. Not because I saw the assumptions in some of my previous pieces undermined (well, ok: yes, that too), but mostly because of the implications for policy. Sure, this is just one paper. As always in science, more research is needed. But policymakers in this field – driven by the strong populist anti-migration movements in Europe – seem to be moving at a different pace.

The new is likely to record sums in development aid to “migration”. In other words: European tax revenue will be earmarked for development projects that will be designed to have an impact on migration. This could mean funding to repatriate stranded migrants from Libya, or to train customs officers in the Sahel, or to invest in job creation projects for "potential migrants" in home countries such as Burkina Faso. 

Academics and experts have lost a potent weapon from their arsenal: much of the criticism of policies linking aid to migration relied on assumptions from migration hump theory

For all sorts of reasons, experts are concerned about these efforts to link foreign aid and migration. They believe that doing so may compromise the benefits of aid for those who need it most. Why? Under the terms favoured in Brussels, for example, European aid could be allocated to dubious border control projects. Budgets could be allocated so that “potential” migrants’ take precedence over “the poorest of the poor”.

Making European support conditional on curbing migration could obstruct or impose limits on seasonal migration, often a main source of income for regional migrants. And countries where emigration is high would be prioritised over lower-migration countries that may have more urgent needs. 

Experts have relied on migration hump theory as a great weapon in their arsenal of academic evidence deployed in these arguments over policy. Because of the migration hump, they countered, the current trend of linking aid to migration would fail to achieve the goal of reducing the influx of migrants in Europe. Because more development would lead to more migration. 

Now the migration hump is discredited by this paper, there’s a significant risk that European policymakers will seize the opportunity – enthusiastically – to refute their critics: “Aha! See, I told you so! Development aid can be a tool to help us curb migration!” 

Other academics, to whom I spoke about this paper, are deeply afraid that this will happen. The researchers themselves share that concern: “In my view, it is not desirable to link development aid to migration goals,” Schneiderheinze told me. “That’s certainly not what we want to achieve with this paper.” 

The final section of the paper anticipates just such an outcome with a cautionary sentence: “Given the reasonably small size of the effect and the struggle of development cooperation to sustainably increase economic growth, the scope to affect migration through this channel remains limited.” 

Does that sentence offer sufficient counterweight to the disruptive impact of the new figures? I doubt it.

Translated from Dutch by Joy Phillips. You can also read the of the article.

Dig deeper

Diagram showing the different money paths and institutions involved in the migration funding that the three journalists tried to unravel in their investigation.
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