Modelling migration

Modelling migration

Public perception of migration revolves very much around the image of Africans leaving their continent en masse to come to the European shores of the Mediterranean in search of jobs and/or a better life.  This image is largely propagated by media reporting of the issue and the failure to present statistics on migration in their proper context.  This is all exacerbated by the prevailing stereotype of Africa being a continent riven by poverty and violence.

The truth is very different.

On 28 June 2017, Rafael Prieto Curiel, Nikoleta Kalaydzhieva and I took ourselves to the Greenwich Maths Time festival at the University of Greenwich with a bed sheet, 23 weights and lots of chickpeas.  On the bed sheet was painted the map of Africa (very artistically so, we’re sure you’d agree) and the weights represented 23 of the largest cities on the continent.  We were there to demonstrate how Newton’s law of gravity can be used to model migration, with migrants being attracted by the size of a city and their distance away from it.  The weights created valleys of attraction on the map, and the chickpeas, when dropped, either moved towards their nearest cities or stayed put.

Although a simplified model, this agrees with what happens in real life.  Most migration occurs from one town or city to a neighbouring city: certainly, it is predominantly intra-continental rather than inter-continental.  Furthermore, the dialogue around migration, and the focus on African migrants, is highly skewed and leads to a huge misconception about its magnitude.  At the festival, we asked those we talked to (mainly secondary school and sixth form students) two questions: if I take 100 Africans, how many of these currently live outside Africa; and out of 100 Europeans, how many currently live outside Europe?

Almost unanimously, people believed that there were comparatively more Africans living out of Africa than Europeans out of Europe, and the numbers quoted were worryingly large.  The reality is that out of 100 Europeans, 3.2 live outside Europe; out of 100 Africans, only 1.4 live outside Africa.  Furthermore, the continent is home to some of the largest cities in the world: Lagos and Cairo have populations approaching 20 million.

Hopefully, we were able to go some way towards changing the perceptions of some of the people we spoke to, and encouraged them to seek out the data behind the stories rather than blindly accepting commonly-held beliefs.  Mathematical models provide us with a powerful tool to understand and predict both natural phenomena and social behaviours; and indicate that the truth is not necessarily counterintuitive.

You can find out more about mathematical models of migration in our Chalkdust article here.

(Data taken from the United Nations Department for Economic and Social Affairs database, Trends in International Migrant Stock: Migrants by destination and origin, updated in 2015.)