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The main reason for an unbalanced sex ratio in most countries is gender-selective migration. Without sex-selective international migration, country-level sex ratios for young adults would be balanced in almost all countries of the world. Michał Gulczyński, a Bocconi University PhD student in Public Policy and Administration, has recently published an article (“Migration and Skewed Subnational Sex Ratios among Young Adults”) on Population and Development Review in which he looks at the causes and the extent of local variations of sex ratios among the crucial age group of young adults between 25 and 34.

Sex ratio is a key parameter of a population. It has to be kept near its equilibrium as a skewed ratio is bound to have potentially very negative impacts on societies in terms, among other things, of criminality and economic development. And even when the sex ratio looks normal at national level, this might not apply at local level within a country nor for all age groups.

There are three possible reasons behind a locally skewed sex ratio. The first is an abnormal prevalence at birth, reflecting gender-selective abortions, the second is higher survival rates for one gender compared with the other, and the third is gender-specific migration. This particular driver of imbalance is due to the fact that women (except in Africa) tend to migrate to cities and men to stay in the countryside. For instance, the rural sex ratio for young adults of 1.27 in Greece means that there are 27 more young men per every 100 women in rural areas, a big disproportion.

“My study is the first global assessment of subnational sex ratio among young adults, and reveals a strong relationship between population density and sex ratios. It shows that local sex ratios—and, by extension, marriage markets—are commonly imbalanced”, says Michał Gulczyński. “The global picture helps to realize how international and inter-regional migration flows influence sex ratios. I also propose a simple and informative way to analyze spatial distribution of population by relating population composition to population density.”

Gulczyński adds, “My initial idea for this paper, which is part of my PhD dissertation, was developed with many top scholars in sociology and demography who work at Bocconi, notably Francesco Billari, who encouraged me and provided me with precious advice.”

Michał Gulczyński, “Migration and Skewed Subnational Sex Ratios among Young Adults”, Population and Development Review, first published 12 July 2023, https://doi.org/10.1111/padr.1257