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Cities鈥� attraction of talent escalates the regional. Photo credit iStock franswillemblok. 鈥淥ur research shows that people who leave rural areas for cities are, on average, better educated and have higher cognitive abilities. This selective migration fuels the higher than expected outputs of big cities and, at the same time, adds to the cumulative decline of less populated regions鈥� says Dr. Marc Keuschnigg, the lead author from Link枚ping University鈥檚 Institute for Analytical Sociology.

Thus, selective migration of highly productive individuals to cities explains a substantial part of urban growth, according to the Link枚ping researchers鈥� study.

The +15% phenomenon of urban life

Marc Keuschnigg. Photo credit: Mikael S枚nne
Urban scaling is an influential research field that analyzes the benefits and detriments of city life. It demonstrates that cities鈥� levels of wealth, innovation, crime, and contagious disease follow highly predictable patterns grounded in population size. This line of research has established that population size is the single most important factor in the functioning of cities, and that many social and economic indicators increase not simply proportionally to city size but are subject to nonlinear dynamics: doubling city size, for example, reportedly raises total income, the number of patents, the number of residential moves, and the number of romantic breakups by roughly 115%鈥攕uggesting that urbanites鈥� productivity and pace of life increase as their cities grow. The extra 15% is referred to as 鈥渟uperlinear scaling鈥� or the +15% phenomenon.

The mathematical models proposed to account for these regularities suggest that superlinear scaling of urban outputs is a consequence of increased social interaction in dense urban environments. In large cities, there are more people to exchange ideas with, as well as to cooperate with in bringing about innovations, new forms of social life, and additional wealth. Consequently, urban scaling researchers see the +15% phenomenon as a self-reinforcing process that produces winners but no losers, implying that urban growth is socially beneficial to contemporary societies in general.

Urban populations and rural flight

Utilizing Swedish register data with unique granularity, the study tests whether the +15% phenomenon truly can be attributed to increased social interconnectivity in cities. Advanced societies exhibit strong and highly selective internal migration. In Sweden, the better educated and more intelligent are most likely to leave rural areas and move to the largest cities Stockholm (in the country鈥檚 east), Gothenburg, or Malm枚 (both in the south). The gray ties indicate migration flows from smaller to relatively larger labor market areas in 2012.

Their geocoded micro-data capture the dissimilarities in the population composition between metropolitan areas of different size and provide better information on the micro-mechanisms responsible for observed nonlinearities.The group鈥檚 research finds that social interactions explain only half of the previously reported agglomeration effects and, in contrast to existing explanations of superlinear urban scaling, they find that differences in population characteristics between metropolitan areas crucially drive the phenomenon.

鈥淥ur results are of considerable policy relevance, because they identify the migration of talented people from smaller areas to larger cities as an important force behind observed agglomeration effects鈥� says Dr. Marc Keuschnigg.

Those moving from smaller areas to one of Sweden鈥檚 larger cities have, on average, 1.8 more years of education and their cognitive ability (measured for men in a standardized test during military conscription) is 0.4 standard deviations higher than for those who stayed. This is consequential for societies because strongly selective migration has cumulative effects on local populations in both sending and receiving regions.

Article:
, Marc Keuschnigg, Selcan Mutgan, Peter Hedstr枚m (2019). Science Advances 5: eaav0042, DOI: 10.1126/sciadv.aav0042